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I am deploying a few different docker containers, mysql being the first one. I want to run scripts as soon as database is up and proceed to building other containers. The script has been failing because it was trying to run when the entrypoint script, which sets up mysql (from this official mysql container), was still running.
sudo docker run --name mysql -e MYSQL_ROOT_PASSWORD=MY_ROOT_PASS -p 3306:3306 -d mysql
[..] wait for mysql to be ready [..]
mysql -h 127.0.0.1 -P 3306 -u root --password=MY_ROOT_PASS < MY_SQL_SCRIPT.sql
Is there a way to wait for a signal of an entrypoiny mysql setup script finishing inside the docker container? Bash sleep seems like a suboptimal solution.
EDIT: Went for a bash script like this. Not the most elegant and kinda brute force but works like a charm. Maybe someone will find that useful.
OUTPUT="Can't connect"
while [[ $OUTPUT == *"Can't connect"* ]]
do
OUTPUT=$(mysql -h $APP_IP -P :$APP_PORT -u yyy --password=xxx < ./my_script.sql 2>&1)
done
You can install mysql-client package and use mysqladmin to ping target server. Useful when working with multiple docker container. Combine with sleep and create a simple wait-loop:
while ! mysqladmin ping -h"$DB_HOST" --silent; do
sleep 1
done
This little bash loop waits for mysql to be open, shouldn't require any extra packages to be installed:
until nc -z -v -w30 $CFG_MYSQL_HOST 3306
do
echo "Waiting for database connection..."
# wait for 5 seconds before check again
sleep 5
done
This was more or less mentioned in comments to other answers, but I think it deserves its own entry.
First of all you can run your container in the following manner:
docker run --name mysql --health-cmd='mysqladmin ping --silent' -d mysql
There is also an equivalent in the Dockerfile.
With that command your docker ps and docker inspect will show you health status of your container. For mysql in particular this method has the advantage of mysqladmin being available inside the container, so you do not need to install it on the docker host.
Then you can simply loop in a bash script to wait on the status to become healthy. The following bash script is created by Dennis.
function getContainerHealth {
docker inspect --format "{{.State.Health.Status}}" $1
}
function waitContainer {
while STATUS=$(getContainerHealth $1); [ $STATUS != "healthy" ]; do
if [ $STATUS == "unhealthy" ]; then
echo "Failed!"
exit -1
fi
printf .
lf=$'\n'
sleep 1
done
printf "$lf"
}
Now you can do this in your script:
waitContainer mysql
and your script will wait until the container is up and running. The script will exit if the container becomes unhealthy, which is possible, if for example docker host is out of memory, so that the mysql cannot allocate enough of it for itself.
I've found that using the mysqladmin ping approach isn't always reliable, especially if you're bringing up a new DB. In that case, even if you're able to ping the server, you might be unable to connect if the user/privilege tables are still being initialized. Instead I do something like the following:
while ! docker exec db-container mysql --user=foo --password=bar -e "SELECT 1" >/dev/null 2>&1; do
sleep 1
done
So far I haven't encountered any problems with this method. I see that something similar was suggested by VinGarcia in a comment to one of the mysqladmin ping answers.
Some times the problem with the port is that the port could be open, but the database is not ready yet.
Other solutions require that you have installed the mysql o a mysql client in your host machine, but really you already have it inside the Docker container, so I prefer to use something like this:
Option 1:
while ! docker exec mysql mysqladmin --user=root --password=pass --host "127.0.0.1" ping --silent &> /dev/null ; do
echo "Waiting for database connection..."
sleep 2
done
Option 2 (from #VinGarcia):
while ! docker exec container_name mysql --user=root --password=pass -e "status" &> /dev/null ; do
echo "Waiting for database connection..."
sleep 2
done
One liner using curl, found on all linux distributions:
while ! curl -o - db-host:3306; do sleep 1; done
The following health-check works for all my mysql containers:
db:
image: mysql:5.7.16
healthcheck:
test: ["CMD-SHELL", 'mysql --database=$$MYSQL_DATABASE --password=$$MYSQL_ROOT_PASSWORD --execute="SELECT count(table_name) > 0 FROM information_schema.tables;" --skip-column-names -B']
interval: 30s
timeout: 10s
retries: 4
extends:
file: docker-compose-common-config.yml
service: common_service
So I am not sure if any one has posted this. It doesn't look like any one has, so... there is a command in mysqladmin that features a wait, it handles testing of the connection, then retries internally and returns a success upon completion.
sudo docker run --name mysql -e MYSQL_ROOT_PASSWORD=MY_ROOT_PASS -p 3306:3306 -d mysql
mysqladmin ping -h 127.0.0.1 -u root --password=MY_ROOT_PASS --wait=30 && mysql -h 127.0.0.1 -P 3306 -u root --password=MY_ROOT_PASS < MY_SQL_SCRIPT.sql
The important piece is mysqladmin ping -h 127.0.0.1 -u root --password=MY_ROOT_PASS --wait=30 -v with the --wait being the flag to wait until the connection is successful and the number being the amount of attempts to retry.
Ideally you would run that command from inside the docker container, but I didn't want to modify the original posters command too much.
When used in my make file for initialization
db.initialize: db.wait db.initialize
db.wait:
docker-compose exec -T db mysqladmin ping -u $(DATABASE_USERNAME) -p$(DATABASE_PASSWORD) --wait=30 --silent
db.initialize:
docker-compose exec -T db mysql -u $(DATABASE_USERNAME) -p$(DATABASE_PASSWORD) $(DATABASE_NAME) < dev/sql/base_instance.sql
I had the same issue when my Django container tried to connect the mysql container just after it started. I solved it using the vishnubob's wait-for.it.sh script. Its a shell script which waits for an IP and a host to be ready before continuing. Here is the example I use for my applicaction.
./wait-for-it.sh \
-h $(docker inspect --format '{{ .NetworkSettings.IPAddress }}' $MYSQL_CONTAINER_NAME) \
-p 3306 \
-t 90
In that script I'm asking to the mysql container to wait maximum 90 seconds (it will run normally when ready) in the port 3306 (default mysql port) and the host asigned by docker for my MYSQL_CONTAINER_NAME. The script have more variables but for mw worked with these three.
If the docker container waiting for a mysql container is based on a python image (for instance for a Django application), you can use the code below.
Advantages are:
It's not based on wait-for-it.sh, which does wait for the IP and port of mysql to be ready, but this doesn't automatically mean also that the mysql initialization has finished.
It's not a shell script based on a mysql or mysqladmin executable that must be present in your container: since your container is based on a python image, this would require installing mysql on top of that image. With the below solution, you use the technology that is already present in the container: pure python.
Code:
import time
import pymysql
def database_not_ready_yet(error, checking_interval_seconds):
print('Database initialization has not yet finished. Retrying over {0} second(s). The encountered error was: {1}.'
.format(checking_interval_seconds,
repr(error)))
time.sleep(checking_interval_seconds)
def wait_for_database(host, port, db, user, password, checking_interval_seconds):
"""
Wait until the database is ready to handle connections.
This is necessary to ensure that the application docker container
only starts working after the MySQL database container has finished initializing.
More info: https://docs.docker.com/compose/startup-order/ and https://docs.docker.com/compose/compose-file/#depends_on .
"""
print('Waiting until the database is ready to handle connections....')
database_ready = False
while not database_ready:
db_connection = None
try:
db_connection = pymysql.connect(host=host,
port=port,
db=db,
user=user,
password=password,
charset='utf8mb4',
connect_timeout=5)
print('Database connection made.')
db_connection.ping()
print('Database ping successful.')
database_ready = True
print('The database is ready for handling incoming connections.')
except pymysql.err.OperationalError as err:
database_not_ready_yet(err, checking_interval_seconds)
except pymysql.err.MySQLError as err:
database_not_ready_yet(err, checking_interval_seconds)
except Exception as err:
database_not_ready_yet(err, checking_interval_seconds)
finally:
if db_connection is not None and db_connection.open:
db_connection.close()
Usage:
Add this code into a python file (wait-for-mysql-db.py for instance) inside your application's source code.
Write another python script (startup.py for instance) that first executes the above code, and afterwards starts up your application.
Make sure your application container's Dockerfile packs these two python scripts together with the application's source code into a Docker image.
In your docker-compose file, configure your application container with: command: ["python3", "startup.py"].
Note that this solution is made for a MySQL database. You'll need to adapt it slightly for another database.
I developed a new solution for this issue based on a new approach. All approaches I found rely on a script that tries over and over to connect to the database, or try to establish a TCP connection with the container. The full details can be found on the waitdb repository, but, my solution is to rely on the retrieved log from the container. The script waits until the log fires the message ready for connections. The script can identify if the container is starting for the first time. In this case the script waits until the initial database script is executed and the database is restarted, waiting again for a new ready for connections message. I tested this solution on MySQL 5.7 and MySQL 8.0.
The script itself (wait_db.sh):
#!/bin/bash
STRING_CONNECT="mysqld: ready for connections"
findString() {
($1 logs -f $4 $5 $6 $7 $8 $9 2>&1 | grep -m $3 "$2" &) | grep -m $3 "$2" > /dev/null
}
echo "Waiting startup..."
findString $1 "$STRING_CONNECT" 1 $2 $3 $4 $5 $6 $7
$1 logs $2 $3 $4 $5 2>&1 | grep -q "Initializing database"
if [ $? -eq 0 ] ; then
echo "Almost there..."
findString $1 "$STRING_CONNECT" 2 $2 $3 $4 $5 $6 $7
fi
echo "Server is up!"
The script can be used in Docker Compose or in Docker itself. I hope the examples bellow make the the usage clear:
Example 01: Using with Docker Compose
SERVICE_NAME="mysql" && \
docker-compose up -d $SERVICE_NAME && \
./wait_db.sh docker-compose --no-color $SERVICE_NAME
Example 02: Using with Docker
CONTAINER_NAME="wait-db-test" && \
ISO_NOW=$(date -uIs) && \
docker run --rm --name $CONTAINER_NAME \
-e MYSQL_ROOT_PASSWORD=$ROOT_PASSWORD \
-d mysql:5.7 && \
./wait_db.sh docker --since "$ISO_NOW" $CONTAINER_NAME
Example 3: A full example (the test-case)
A full example can be found on the test case of the repository. This test-case will startup a new MySQL, create a dummy database, wait until everything is started and then fires a select to check if everything goes fine. After that it'll going restart the container and wait it to be started and then fires a new select to check if it's ready for connection.
Here's how I incorporated Adams solution into my docker-compose based project:
Created a bash file titled db-ready.sh in my server container folder (the contents of which are copied in to my container - server):
#!bin/bash
until nc -z -v -w30 $MYSQL_HOST 3306
do
echo "Waiting a second until the database is receiving connections..."
# wait for a second before checking again
sleep 1
done
I can then run docker-compose run server sh ./db-ready.sh && docker-compose run server yarn run migrate to ensure that when I run my migrate task within my server container, I know the DB will be accepting connections.
I like this approach as the bash file is separate to any command I want to run. I could easily run the db-ready.sh before any other DB using task I run.
i can recommend you to use /usr/bin/mysql --user=root --password=root --execute "SHOW DATABASE;" in healthcheck script instead of mysqladmin ping. This wait for real initialization and service is ready for client connection.
Example:
docker run -d --name "test-mysql-client" -p 0.0.0.0:3306:3306 -e MYSQL_PASSWORD=password -e MYSQL_USER=user -e MYSQL_ROOT_PASSWORD=root --health-cmd="/usr/bin/mysql --user=root --password=root --execute \"SHOW DATABASE;\"" --health-interval=1s --health-retries=60 --health-timeout=10s -e MYSQL_DATABASE=db mysql:latest```
Combining flamemyst‘s answer and Nathan Arthur's comment, I believe this answer would be the most convenient one:
CONTAINER_MYSQL='' # name of the MySQL container
CONTAINER_DB_HOST='127.0.0.1'
CONTAINER_DB_PORT=3306
MYSQL_USER='' # user name if there is, normally 'root'
MYSQL_PWD='' # password you set
is_mysql_alive() {
docker exec -it ${CONTAINER_MYSQL} \
mysqladmin ping \
--user=${MYSQL_USER} \
--password=${MYSQL_PWD} \
--host=${CONTAINER_DB_HOST} \
--port=${CONTAINER_DB_PORT} \
> /dev/null
returned_value=$?
echo ${returned_value}
}
until [ "$(is_mysql_alive)" -eq 0 ]
do
sleep 2
echo "Waiting for MySQL to be ready..."
done
anything_else_to_do
Basically, it checks whether mysqladmin is alive in MySQL container, MySQL should be up if so.
Building a bit on Mihai Crăiță excellent answer above, I added in the CURL option to enable 0.9 (which is disabled by default now) and to hide the output to reduce log "noise" during startup:
server="MyServerName"
echo "Waiting for MySQL at ${server}"
while ! curl --http0.9 -o - "${server}:3306" &> /dev/null; do sleep 1; done
https://github.com/docker-library/mysql/blob/master/5.7/docker-entrypoint.sh
docker-entrypoint.sh doesn't support merging customized .sql yet.
I think you can modify docker-entrypoint.sh to merge your sql so it can be executed once mysql instance is ready.
On your ENTRYPOINT script, you have to check if you have a valid MySQL connection or not.
This solution does not require you to install a MySQL Client on the container and while running the container with php:7.0-fpm running nc was not an option, because it had to be installed as well. Also, checking if the port is open does not necessarily mean that the service is running and exposed correctly. [more of this]
So in this solution, I will show you how to run a PHP script to check if a MySQL Container is able to take connection. If you want to know why I think this is a better approach check my comment here.
File entrypoint.sh
#!/bin/bash
cat << EOF > /tmp/wait_for_mysql.php
<?php
\$connected = false;
while(!\$connected) {
try{
\$dbh = new pdo(
'mysql:host=mysql:3306;dbname=db_name', 'db_user', 'db_pass',
array(PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION)
);
\$connected = true;
}
catch(PDOException \$ex){
error_log("Could not connect to MySQL");
error_log(\$ex->getMessage());
error_log("Waiting for MySQL Connection.");
sleep(5);
}
}
EOF
php /tmp/wait_for_mysql.php
# Rest of entry point bootstrapping
By running this, you are essentially blocking any bootstrapping logic of your container UNTIL you have a valid MySQL Connection.
I use the following code ;
export COMPOSE_PROJECT_NAME=web;
export IS_DATA_CONTAINER_EXISTS=$(docker volume ls | grep ${COMPOSE_PROJECT_NAME}_sqldata);
docker-compose up -d;
docker-compose ps;
export NETWORK_GATEWAY=$(docker inspect --format='{{range .NetworkSettings.Networks}}{{.Gateway}}{{end}}' ${COMPOSE_PROJECT_NAME}_webserver1_con);
Hi I am using the terminal under Linux
I am trying to analyse mysql packets sent in response to some simple queries.
I can see the queries with the command
tshark -i any -d tcp.port==3306,mysql -T fields -e mysql.query 'port 3306'
and I can also see the responses (numbers not content) sent from mysql using
tshark -i any -d tcp.port==3306,mysql 'port 3306'
i.e
1 0.000000000 89.200.139.212 -> 127.0.0.1 MySQL 89 Request Query
2 0.000199026 127.0.0.1 -> 127.0.0.1 MySQL 79 Response OK
3 0.000310118 89.200.139.212 -> 127.0.0.1 TCP 68 33170 > mysql [ACK] Seq=22 Ack=12 Win=11256
Is there some way I can see the queries sent and see the byte array of the responses sent back from MySQL on the terminal at the same time?
so I can see the which bytes are sent in response to which sql queries.
In the end, I used the command
tshark -i any -d tcp.port==3306,mysql -T fields -e mysql.query -e mysql.payload 'port 3306'
Because we develop using remote Mysql server , so cannot check query sql easily, if use local server you can tail - f general_log_file to see which sql are executed when call some http interface. So I installed a wireshark to capture these query sql send from local. At first I use local mysql to verify it.
The capture filter is
then I executed two query sql in mysql terminal
select version();
select now();
but very disappointing I cannot find these two sql packets in wireshark
I only found these four packets.
But from a post I knew
To filter out the mysql packets you just use the filter ‘mysql‘ or ‘mysql.query != “”‘ when you only want packets that request a query. After that you can add a custom column with the field name ‘mysql.query’ to have a list of queries that where executed.
and the effect is like this
It's convenient to capture only query sql and very clearly displayed these query sql. So how could I use wireshark to implement this?
hi #Jeff S.
I tried your command, please see below
#terminal 1
tshark -i lo0 -Y "mysql.command==3"
Capturing on 'Loopback'
# terminal 2
mysql -h127.0.0.1 -u root -p
select version();
#result: nothing output in terminal 1
and tshark -i lo0 -Y "mysql.command==3" -T fields -e mysql.query is same with tshark -i lo -Y "mysql.command==3" also nothing output. But if I only use tshark -i lo0, it has output
Capturing on 'Loopback'
1 0.000000 127.0.0.1 -> 127.0.0.1 TCP 68 57881 → 3306 [SYN] Seq=0 Win=65535 Len=0 MSS=16344 WS=32 TSval=1064967501 TSecr=0 SACK_PERM=1
2 0.000062 127.0.0.1 -> 127.0.0.1 TCP 68 3306 → 57881 [SYN, ACK] Seq=0 Ack=1 Win=65535 Len=0 MSS=16344 WS=32 TSval=1064967501 TSecr=1064967501 SACK_PERM=1
3 0.000072 127.0.0.1 -> 127.0.0.1 TCP 56 57881 → 3306 [ACK] Seq=1 Ack=1 Win=408288 Len=0 TSval=1064967501 TSecr=1064967501
4 0.000080 127.0.0.1 -> 127.0.0.1 TCP 56 [TCP Window Update] 3306 → 57881 [ACK] Seq=1 Ack=1 Win=408288 Len=0 TSval=1064967501 TSecr=1064967501
...
You can use tshark and save to a pcap or just export the fields you're interested in.
To save to a pcap (if you want to use wireshark to view later):
tshark -i lo -Y "mysql.command==3" -w outputfile.pcap
tshark -i lo -R "mysql.command==3" -w outputfile.pcap
-R is deprecated for single pass filters, but it will depend on your version
-i is interface so replace that with whatever interface you are using (e.g -i eth0)
To save to a text file:
tshark -i lo -Y "mysql.command==3" -T fields -e mysql.query > output.txt
You can also use BPF filters with tcpdump (and wireshark pre cap filters). They are more complex, but less taxing on your system if you're capturing a lot of traffic.
sudo tcpdump -i lo "dst port 3306 and tcp[(((tcp[12:1]&0xf0)>>2)+4):1]=0x03" -w outputfile.pcap
NOTE:
*This looks for 03 (similar mysql.command==3) within the TCP payload.
**Since this is a pretty loose filter, I also added 3306 to restrict to only traffic destined for that port.
***The filter is based on your screenshot. I cannot validate it right now so let me know if it doesn't work.
Example Output:
Useful answers here:
https://serverfault.com/questions/358978/how-to-capture-the-queries-run-on-mysql-server
In particular: SoMoSparky's answer of:
tshark -T fields -R mysql.query -e mysql.query
and user1038090's answer of:
tcpdump -i any -s 0 -l -vvv -w - dst port 3306 | strings | perl -e '
while(<>) { chomp; next if /^[^ ]+[ ]*$/;
if(/^(SELECT|UPDATE|DELETE|INSERT|SET|COMMIT|ROLLBACK|CREATE|DROP|ALTER)/i) {
if (defined $q) { print "$q\n"; }
$q=$_;
} else {
$_ =~ s/^[ \t]+//; $q.=" $_";
}
}'
I had similar "problem"
Try to check your mysql ssl
Probably the ssl was turned on hence the traffic was encrypted
You can refer to this post to check the ssl: https://dba.stackexchange.com/questions/36776/how-can-i-verify-im-using-ssl-to-connect-to-mysql
I tried another tshark command from this post, and it could capture query sql from local to remote mysql server.
tshark -i en0 -d tcp.port==3306,mysql -T fields -e mysql.query 'port 3306'
Capturing on 'Wi-Fi'
select version()
select now()
select rand()
but it also output some blank lines between these sql. I tried below command want to remove blank line but failed
tshark -i en0 -d tcp.port==6006,mysql -Y "frame.len>10" -T fields -e mysql.query 'port 6006'
And unfortunately this command cannot support capturing query sql to local mysql(5.7.12).
tshark -i lo -d tcp.port==3306,mysql -T fields -e mysql.query 'port 3306'
Capturing on 'Loopback'
Nothing output except blank lines.
Wireshark tool supports MySQL protocol:
https://www.wireshark.org/docs/dfref/m/mysql.html
Then config wireshark
a.menu Analyze --> Decode as --> add "field=tcp_port value=3306 current=MySQL"
b.filter ‘mysql‘ or ‘mysql.query != “”‘
Error while executing ansible ping module
bash ~ ansible webservers -i inventory -m ping -k -u root -vvvv
SSH password:
<~> ESTABLISH CONNECTION FOR USER: root on PORT 22 TO ~
<my-lnx> ESTABLISH CONNECTION FOR USER: root on PORT 22 TO my-lnx
~ | FAILED => FAILED: [Errno 8] nodename nor servname provided, or not known
<my-lnx> REMOTE_MODULE ping
<my-lnx> EXEC /bin/sh -c 'mkdir -p $HOME/.ansible/tmp/ansible-tmp-1423302966.66-77716810353582 && echo $HOME/.ansible/tmp/ansible-tmp-1423302966.66-77716810353582'
<my-lnx> PUT /var/folders/8n/fftvnbbs51q834y16vfvb1q00000gn/T/tmpP6zwZj TO /root/.ansible/tmp/ansible-tmp-1423302966.66-77716810353582/ping
<my-lnx> EXEC /bin/sh -c 'LANG=en_US.UTF-8 LC_CTYPE=en_US.UTF-8 /usr/bin/python /root/.ansible/tmp/ansible-tmp-1423302966.66-77716810353582/ping; rm -rf /root/.ansible/tmp/ansible-tmp-1423302966.66-77716810353582/ >/dev/null 2>&1'
my-lnx | FAILED >> {
"failed": true,
"msg": "Error: ansible requires a json module, none found!",
"parsed": false
}
This is my inventory file
bash ~ cat inventory
[webservers]
my-lnx ansible_ssh_host=my-lnx ansible_ssh_port=22
I have installed simplejosn module also in the client as well as remote machine
bash ~ pip list | grep json
simple-json (1.1)
simplejson (3.6.5)
I think you need to install the python-simplejson module.
Try to run this command first and then your desired commands:
ansible webservers -i inventory -m raw -a "sudo yum install -y python-simplejson" -k -u root -vvvv
I am supposing that its old Red Hat/CentOS system.
If you don't want or can't install the python-simplejson module on remote servers, you can simply request the raw output instead:
> ansible webservers -i inventory -m ping -m raw
Or like I did, added it to my ~/.bash_profile
alias ansible="ansible -m raw"
# And then simply running:
> ansible webservers -i inventory -m ping
in centos 5.* version no python-simple json available on repo to donwload and install. you can simple use below mentioned method.
make sure both the source and destination should be accessed password less and from source to destination also password less.
use ssh-keygen -t rsa to generate key
ssh-copy-id user#host_ip
"---
- hosts: (ansible host)
become: yes
remote_user: root
gather_facts: false
tasks:
- name: copying copying temps
shell: ssh (source) && rsync -parv /root/temp/* root#(Destination):/root/temp/"
I am deploying a few different docker containers, mysql being the first one. I want to run scripts as soon as database is up and proceed to building other containers. The script has been failing because it was trying to run when the entrypoint script, which sets up mysql (from this official mysql container), was still running.
sudo docker run --name mysql -e MYSQL_ROOT_PASSWORD=MY_ROOT_PASS -p 3306:3306 -d mysql
[..] wait for mysql to be ready [..]
mysql -h 127.0.0.1 -P 3306 -u root --password=MY_ROOT_PASS < MY_SQL_SCRIPT.sql
Is there a way to wait for a signal of an entrypoiny mysql setup script finishing inside the docker container? Bash sleep seems like a suboptimal solution.
EDIT: Went for a bash script like this. Not the most elegant and kinda brute force but works like a charm. Maybe someone will find that useful.
OUTPUT="Can't connect"
while [[ $OUTPUT == *"Can't connect"* ]]
do
OUTPUT=$(mysql -h $APP_IP -P :$APP_PORT -u yyy --password=xxx < ./my_script.sql 2>&1)
done
You can install mysql-client package and use mysqladmin to ping target server. Useful when working with multiple docker container. Combine with sleep and create a simple wait-loop:
while ! mysqladmin ping -h"$DB_HOST" --silent; do
sleep 1
done
This little bash loop waits for mysql to be open, shouldn't require any extra packages to be installed:
until nc -z -v -w30 $CFG_MYSQL_HOST 3306
do
echo "Waiting for database connection..."
# wait for 5 seconds before check again
sleep 5
done
This was more or less mentioned in comments to other answers, but I think it deserves its own entry.
First of all you can run your container in the following manner:
docker run --name mysql --health-cmd='mysqladmin ping --silent' -d mysql
There is also an equivalent in the Dockerfile.
With that command your docker ps and docker inspect will show you health status of your container. For mysql in particular this method has the advantage of mysqladmin being available inside the container, so you do not need to install it on the docker host.
Then you can simply loop in a bash script to wait on the status to become healthy. The following bash script is created by Dennis.
function getContainerHealth {
docker inspect --format "{{.State.Health.Status}}" $1
}
function waitContainer {
while STATUS=$(getContainerHealth $1); [ $STATUS != "healthy" ]; do
if [ $STATUS == "unhealthy" ]; then
echo "Failed!"
exit -1
fi
printf .
lf=$'\n'
sleep 1
done
printf "$lf"
}
Now you can do this in your script:
waitContainer mysql
and your script will wait until the container is up and running. The script will exit if the container becomes unhealthy, which is possible, if for example docker host is out of memory, so that the mysql cannot allocate enough of it for itself.
I've found that using the mysqladmin ping approach isn't always reliable, especially if you're bringing up a new DB. In that case, even if you're able to ping the server, you might be unable to connect if the user/privilege tables are still being initialized. Instead I do something like the following:
while ! docker exec db-container mysql --user=foo --password=bar -e "SELECT 1" >/dev/null 2>&1; do
sleep 1
done
So far I haven't encountered any problems with this method. I see that something similar was suggested by VinGarcia in a comment to one of the mysqladmin ping answers.
Some times the problem with the port is that the port could be open, but the database is not ready yet.
Other solutions require that you have installed the mysql o a mysql client in your host machine, but really you already have it inside the Docker container, so I prefer to use something like this:
Option 1:
while ! docker exec mysql mysqladmin --user=root --password=pass --host "127.0.0.1" ping --silent &> /dev/null ; do
echo "Waiting for database connection..."
sleep 2
done
Option 2 (from #VinGarcia):
while ! docker exec container_name mysql --user=root --password=pass -e "status" &> /dev/null ; do
echo "Waiting for database connection..."
sleep 2
done
One liner using curl, found on all linux distributions:
while ! curl -o - db-host:3306; do sleep 1; done
The following health-check works for all my mysql containers:
db:
image: mysql:5.7.16
healthcheck:
test: ["CMD-SHELL", 'mysql --database=$$MYSQL_DATABASE --password=$$MYSQL_ROOT_PASSWORD --execute="SELECT count(table_name) > 0 FROM information_schema.tables;" --skip-column-names -B']
interval: 30s
timeout: 10s
retries: 4
extends:
file: docker-compose-common-config.yml
service: common_service
So I am not sure if any one has posted this. It doesn't look like any one has, so... there is a command in mysqladmin that features a wait, it handles testing of the connection, then retries internally and returns a success upon completion.
sudo docker run --name mysql -e MYSQL_ROOT_PASSWORD=MY_ROOT_PASS -p 3306:3306 -d mysql
mysqladmin ping -h 127.0.0.1 -u root --password=MY_ROOT_PASS --wait=30 && mysql -h 127.0.0.1 -P 3306 -u root --password=MY_ROOT_PASS < MY_SQL_SCRIPT.sql
The important piece is mysqladmin ping -h 127.0.0.1 -u root --password=MY_ROOT_PASS --wait=30 -v with the --wait being the flag to wait until the connection is successful and the number being the amount of attempts to retry.
Ideally you would run that command from inside the docker container, but I didn't want to modify the original posters command too much.
When used in my make file for initialization
db.initialize: db.wait db.initialize
db.wait:
docker-compose exec -T db mysqladmin ping -u $(DATABASE_USERNAME) -p$(DATABASE_PASSWORD) --wait=30 --silent
db.initialize:
docker-compose exec -T db mysql -u $(DATABASE_USERNAME) -p$(DATABASE_PASSWORD) $(DATABASE_NAME) < dev/sql/base_instance.sql
I had the same issue when my Django container tried to connect the mysql container just after it started. I solved it using the vishnubob's wait-for.it.sh script. Its a shell script which waits for an IP and a host to be ready before continuing. Here is the example I use for my applicaction.
./wait-for-it.sh \
-h $(docker inspect --format '{{ .NetworkSettings.IPAddress }}' $MYSQL_CONTAINER_NAME) \
-p 3306 \
-t 90
In that script I'm asking to the mysql container to wait maximum 90 seconds (it will run normally when ready) in the port 3306 (default mysql port) and the host asigned by docker for my MYSQL_CONTAINER_NAME. The script have more variables but for mw worked with these three.
If the docker container waiting for a mysql container is based on a python image (for instance for a Django application), you can use the code below.
Advantages are:
It's not based on wait-for-it.sh, which does wait for the IP and port of mysql to be ready, but this doesn't automatically mean also that the mysql initialization has finished.
It's not a shell script based on a mysql or mysqladmin executable that must be present in your container: since your container is based on a python image, this would require installing mysql on top of that image. With the below solution, you use the technology that is already present in the container: pure python.
Code:
import time
import pymysql
def database_not_ready_yet(error, checking_interval_seconds):
print('Database initialization has not yet finished. Retrying over {0} second(s). The encountered error was: {1}.'
.format(checking_interval_seconds,
repr(error)))
time.sleep(checking_interval_seconds)
def wait_for_database(host, port, db, user, password, checking_interval_seconds):
"""
Wait until the database is ready to handle connections.
This is necessary to ensure that the application docker container
only starts working after the MySQL database container has finished initializing.
More info: https://docs.docker.com/compose/startup-order/ and https://docs.docker.com/compose/compose-file/#depends_on .
"""
print('Waiting until the database is ready to handle connections....')
database_ready = False
while not database_ready:
db_connection = None
try:
db_connection = pymysql.connect(host=host,
port=port,
db=db,
user=user,
password=password,
charset='utf8mb4',
connect_timeout=5)
print('Database connection made.')
db_connection.ping()
print('Database ping successful.')
database_ready = True
print('The database is ready for handling incoming connections.')
except pymysql.err.OperationalError as err:
database_not_ready_yet(err, checking_interval_seconds)
except pymysql.err.MySQLError as err:
database_not_ready_yet(err, checking_interval_seconds)
except Exception as err:
database_not_ready_yet(err, checking_interval_seconds)
finally:
if db_connection is not None and db_connection.open:
db_connection.close()
Usage:
Add this code into a python file (wait-for-mysql-db.py for instance) inside your application's source code.
Write another python script (startup.py for instance) that first executes the above code, and afterwards starts up your application.
Make sure your application container's Dockerfile packs these two python scripts together with the application's source code into a Docker image.
In your docker-compose file, configure your application container with: command: ["python3", "startup.py"].
Note that this solution is made for a MySQL database. You'll need to adapt it slightly for another database.
I developed a new solution for this issue based on a new approach. All approaches I found rely on a script that tries over and over to connect to the database, or try to establish a TCP connection with the container. The full details can be found on the waitdb repository, but, my solution is to rely on the retrieved log from the container. The script waits until the log fires the message ready for connections. The script can identify if the container is starting for the first time. In this case the script waits until the initial database script is executed and the database is restarted, waiting again for a new ready for connections message. I tested this solution on MySQL 5.7 and MySQL 8.0.
The script itself (wait_db.sh):
#!/bin/bash
STRING_CONNECT="mysqld: ready for connections"
findString() {
($1 logs -f $4 $5 $6 $7 $8 $9 2>&1 | grep -m $3 "$2" &) | grep -m $3 "$2" > /dev/null
}
echo "Waiting startup..."
findString $1 "$STRING_CONNECT" 1 $2 $3 $4 $5 $6 $7
$1 logs $2 $3 $4 $5 2>&1 | grep -q "Initializing database"
if [ $? -eq 0 ] ; then
echo "Almost there..."
findString $1 "$STRING_CONNECT" 2 $2 $3 $4 $5 $6 $7
fi
echo "Server is up!"
The script can be used in Docker Compose or in Docker itself. I hope the examples bellow make the the usage clear:
Example 01: Using with Docker Compose
SERVICE_NAME="mysql" && \
docker-compose up -d $SERVICE_NAME && \
./wait_db.sh docker-compose --no-color $SERVICE_NAME
Example 02: Using with Docker
CONTAINER_NAME="wait-db-test" && \
ISO_NOW=$(date -uIs) && \
docker run --rm --name $CONTAINER_NAME \
-e MYSQL_ROOT_PASSWORD=$ROOT_PASSWORD \
-d mysql:5.7 && \
./wait_db.sh docker --since "$ISO_NOW" $CONTAINER_NAME
Example 3: A full example (the test-case)
A full example can be found on the test case of the repository. This test-case will startup a new MySQL, create a dummy database, wait until everything is started and then fires a select to check if everything goes fine. After that it'll going restart the container and wait it to be started and then fires a new select to check if it's ready for connection.
Here's how I incorporated Adams solution into my docker-compose based project:
Created a bash file titled db-ready.sh in my server container folder (the contents of which are copied in to my container - server):
#!bin/bash
until nc -z -v -w30 $MYSQL_HOST 3306
do
echo "Waiting a second until the database is receiving connections..."
# wait for a second before checking again
sleep 1
done
I can then run docker-compose run server sh ./db-ready.sh && docker-compose run server yarn run migrate to ensure that when I run my migrate task within my server container, I know the DB will be accepting connections.
I like this approach as the bash file is separate to any command I want to run. I could easily run the db-ready.sh before any other DB using task I run.
i can recommend you to use /usr/bin/mysql --user=root --password=root --execute "SHOW DATABASE;" in healthcheck script instead of mysqladmin ping. This wait for real initialization and service is ready for client connection.
Example:
docker run -d --name "test-mysql-client" -p 0.0.0.0:3306:3306 -e MYSQL_PASSWORD=password -e MYSQL_USER=user -e MYSQL_ROOT_PASSWORD=root --health-cmd="/usr/bin/mysql --user=root --password=root --execute \"SHOW DATABASE;\"" --health-interval=1s --health-retries=60 --health-timeout=10s -e MYSQL_DATABASE=db mysql:latest```
Combining flamemyst‘s answer and Nathan Arthur's comment, I believe this answer would be the most convenient one:
CONTAINER_MYSQL='' # name of the MySQL container
CONTAINER_DB_HOST='127.0.0.1'
CONTAINER_DB_PORT=3306
MYSQL_USER='' # user name if there is, normally 'root'
MYSQL_PWD='' # password you set
is_mysql_alive() {
docker exec -it ${CONTAINER_MYSQL} \
mysqladmin ping \
--user=${MYSQL_USER} \
--password=${MYSQL_PWD} \
--host=${CONTAINER_DB_HOST} \
--port=${CONTAINER_DB_PORT} \
> /dev/null
returned_value=$?
echo ${returned_value}
}
until [ "$(is_mysql_alive)" -eq 0 ]
do
sleep 2
echo "Waiting for MySQL to be ready..."
done
anything_else_to_do
Basically, it checks whether mysqladmin is alive in MySQL container, MySQL should be up if so.
Building a bit on Mihai Crăiță excellent answer above, I added in the CURL option to enable 0.9 (which is disabled by default now) and to hide the output to reduce log "noise" during startup:
server="MyServerName"
echo "Waiting for MySQL at ${server}"
while ! curl --http0.9 -o - "${server}:3306" &> /dev/null; do sleep 1; done
https://github.com/docker-library/mysql/blob/master/5.7/docker-entrypoint.sh
docker-entrypoint.sh doesn't support merging customized .sql yet.
I think you can modify docker-entrypoint.sh to merge your sql so it can be executed once mysql instance is ready.
On your ENTRYPOINT script, you have to check if you have a valid MySQL connection or not.
This solution does not require you to install a MySQL Client on the container and while running the container with php:7.0-fpm running nc was not an option, because it had to be installed as well. Also, checking if the port is open does not necessarily mean that the service is running and exposed correctly. [more of this]
So in this solution, I will show you how to run a PHP script to check if a MySQL Container is able to take connection. If you want to know why I think this is a better approach check my comment here.
File entrypoint.sh
#!/bin/bash
cat << EOF > /tmp/wait_for_mysql.php
<?php
\$connected = false;
while(!\$connected) {
try{
\$dbh = new pdo(
'mysql:host=mysql:3306;dbname=db_name', 'db_user', 'db_pass',
array(PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION)
);
\$connected = true;
}
catch(PDOException \$ex){
error_log("Could not connect to MySQL");
error_log(\$ex->getMessage());
error_log("Waiting for MySQL Connection.");
sleep(5);
}
}
EOF
php /tmp/wait_for_mysql.php
# Rest of entry point bootstrapping
By running this, you are essentially blocking any bootstrapping logic of your container UNTIL you have a valid MySQL Connection.
I use the following code ;
export COMPOSE_PROJECT_NAME=web;
export IS_DATA_CONTAINER_EXISTS=$(docker volume ls | grep ${COMPOSE_PROJECT_NAME}_sqldata);
docker-compose up -d;
docker-compose ps;
export NETWORK_GATEWAY=$(docker inspect --format='{{range .NetworkSettings.Networks}}{{.Gateway}}{{end}}' ${COMPOSE_PROJECT_NAME}_webserver1_con);