Can't connect to db docker container - mysql

Question

currently working on moving our application to start using docker. It's a typical app with backend and frontend. I don't have any troubles with front, while still can't launch back.
I have Docker file for backend:
FROM williamyeh/java8
RUN apt-get -y update && apt-get install -y maven
WORKDIR /explorerbackend
ADD settings.xml /root/.m2/settings.xml
ADD pom.xml /explorerbackend
ADD src /explorerbackend/src
RUN ["mvn", "clean", "install"]
ADD target/explorer-backend-1.0.jar /explorerbackend/app.jar
RUN sh -c 'touch /explorerbackend/app.jar'
ENV JAVA_OPTS=""
ENTRYPOINT [ "sh", "-c", "java $JAVA_OPTS -Djava.security.egd=file:/dev/./urandom -jar /explorerbackend/app.jar" ]
and Docker file for mysql:
FROM mysql
ADD createDB.sql /docker-entrypoint-initdb.d
The reason i'm using a separate Docker file for mysql instead of just using image in docker-compose is necessity to create 2 databases on start (otherwise backend will not launch)
createDB.sql file looks as:
CREATE DATABASE IE;
CREATE DATABASE IE_test;
Now i have docker-compose.yml file which is supposed to start 2 containers and make backend connect to database:
version: "3.0"
services:
database:
environment:
MYSQL_ROOT_PASSWORD: root
build:
context: *PATH_TO_DIR_WITH_DOCKERFILE*
dockerfile: Dockerfile
ports:
- 3306:3306
volumes:
- db_data:/var/lib/mysql
backend:
build:
context: *PATH_TO_DIR_WITH_DOCKERFILE*
dockerfile: Dockerfile
ports:
- 3000:3000
depends_on:
- database
volumes:
db_data:
When I run the command docker-compose up database container is up and running while backend is failing:
backend_1 | java.sql.SQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 3 times. Giving up.
However I'm able to log in to database container and I do see databases created:
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| IE |
| IE_test |
| mysql |
| performance_schema |
| sys |
+--------------------+
6 rows in set (0.00 sec)
The only reason I see might be related to yml property file of backend:
app:
data-base:
name: IE
link: database
port: 3306
.................
From the frontend container I'm able to ping database (but am I allowed to put into property file just link:database):
root#897b187f9042:/frontend# ping database
PING database (172.19.0.2): 56 data bytes
64 bytes from 172.19.0.2: icmp_seq=0 ttl=64 time=0.086 ms
64 bytes from 172.19.0.2: icmp_seq=1 ttl=64 time=0.088 ms
So, I assume it's pingable from backend container as well, but why it's not able to connect to db server?

Answer 1

MySQL takes a few seconds to start-up. In-order to confirm this is a race-condition, try the following:
$ docker-compose up -d database && sleep 5 && docker-compose up
When/if this confirms the race-condition, you can alleviate that with a HEALTHCHECK on your database image.
See: https://github.com/docker-library/healthcheck/tree/master/mysql
Script from above link:
#!/bin/bash
set -eo pipefail
if [ "$MYSQL_RANDOM_ROOT_PASSWORD" ] && [ -z "$MYSQL_USER" ] && [ -z "$MYSQL_PASSWORD" ]; then
# there's no way we can guess what the random MySQL password was
echo >&2 'healthcheck error: cannot determine random root password (and MYSQL_USER and MYSQL_PASSWORD were not set)'
exit 0
fi
host="$(hostname --ip-address || echo '127.0.0.1')"
user="${MYSQL_USER:-root}"
export MYSQL_PWD="${MYSQL_PASSWORD:-$MYSQL_ROOT_PASSWORD}"
args=(
# force mysql to not use the local "mysqld.sock" (test "external" connectibility)
-h"$host"
-u"$user"
--silent
)
if select="$(echo 'SELECT 1' | mysql "${args[#]}")" && [ "$select" = '1' ]; then
exit 0
fi
exit 1

Answer 2

Eventually, we found the problem which is a kind of oversight.
The root cause was backend dockerfile:
FROM williamyeh/java8
RUN apt-get -y update && apt-get install -y maven
WORKDIR /explorerbackend
ADD settings.xml /root/.m2/settings.xml
ADD pom.xml /explorerbackend
ADD src /explorerbackend/src
RUN ["mvn", "clean", "install"]
ADD target/explorer-backend-1.0.jar /explorerbackend/app.jar
RUN sh -c 'touch /explorerbackend/app.jar'
ENV JAVA_OPTS=""
ENTRYPOINT [ "sh", "-c", "java $JAVA_OPTS -Djava.security.egd=file:/dev/./urandom -jar /explorerbackend/app.jar" ]
The idea is pretty simple:
1. Take java image
2. install maven
3. copy src folder of my project from host
4. install with maven in container
5. move jar to workdir inside container
6. launch it
However, option 5. doesn't look correct, as instead of copying jar file what was just created by maven inside container i was copying it from my host.
Issue was resolved simply replacing
ADD target/explorer-backend-1.0.jar /explorerbackend/app.jar
with
RUN cp /explorerbackend/target/explorer-backend-1.0.jar /explorerbackend/app.jar
Thanks Rawcode for looking into it!