I'm trying to wrap my head around Docker from the point of deploying an application which is intended to run on the users on desktop. My application is simply a flask web application and mongo database. Normally I would install both in a VM and, forward a host port to the guest web app. I'd like to give Docker a try but I'm not sure how I'm meant to use more than one program. The documentations says there can only be only ENTRYPOINT so how can I have Mongo and my flask application. Or do they need to be in separate containers, in which case how do they talk to each other and how does this make distributing the app easy?
There can be only one ENTRYPOINT, but that target is usually a script that launches as many programs that are needed. You can additionally use for example Supervisord or similar to take care of launching multiple services inside single container. This is an example of a docker container running mysql, apache and wordpress within a single container.
Say, You have one database that is used by a single web application. Then it is probably easier to run both in a single container.
If You have a shared database that is used by more than one application, then it would be better to run the database in its own container and the applications each in their own containers.
There are at least two possibilities how the applications can communicate with each other when they are running in different containers:
Use exposed IP ports and connect via them.
Recent docker versions support linking.
I strongly disagree with some previous solutions that recommended to run both services in the same container. It's clearly stated in the documentation that it's not a recommended:
It is generally recommended that you separate areas of concern by using one service per container. That service may fork into multiple processes (for example, Apache web server starts multiple worker processes). It’s ok to have multiple processes, but to get the most benefit out of Docker, avoid one container being responsible for multiple aspects of your overall application. You can connect multiple containers using user-defined networks and shared volumes.
There are good use cases for supervisord or similar programs but running a web application + database is not part of them.
You should definitely use docker-compose to do that and orchestrate multiple containers with different responsibilities.
I had similar requirement of running a LAMP stack, Mongo DB and my own services
Docker is OS based virtualisation, which is why it isolates its container around a running process, hence it requires least one process running in FOREGROUND.
So you provide your own startup script as the entry point, thus your startup script becomes an extended Docker image script, in which you can stack any number of the services as far as AT LEAST ONE FOREGROUND SERVICE IS STARTED, WHICH TOO TOWARDS THE END
So my Docker image file has two line below in the very end:
COPY myStartupScript.sh /usr/local/myscripts/myStartupScript.sh
CMD ["/bin/bash", "/usr/local/myscripts/myStartupScript.sh"]
In my script I run all MySQL, MongoDB, Tomcat etc. In the end I run my Apache as a foreground thread.
source /etc/apache2/envvars
/usr/sbin/apache2 -DFOREGROUND
This enables me to start all my services and keep the container alive with the last service started being in the foreground
Hope it helps
UPDATE: Since I last answered this question, new things have come up like Docker compose, which can help you run each service on its own container, yet bind all of them together as dependencies among those services, try knowing more about docker-compose and use it, it is more elegant way unless your need does not match with it.
Although it's not recommended you can run 2 processes in foreground by using wait. Just make a bash script with the following content. Eg start.sh:
# runs 2 commands simultaneously:
mongod & # your first application
P1=$!
python script.py & # your second application
P2=$!
wait $P1 $P2
In your Dockerfile, start it with
CMD bash start.sh
I would recommend to set up a local Kubernetes cluster if you want to run multiple processes simultaneously. You can 'distribute' the app by providing them a simple Kubernetes manifest.
They can be in separate containers, and indeed, if the application was also intended to run in a larger environment, they probably would be.
A multi-container system would require some more orchestration to be able to bring up all the required dependencies, though in Docker v0.6.5+, there is a new facility to help with that built into Docker itself - Linking. With a multi-machine solution, its still something that has to be arranged from outside the Docker environment however.
With two different containers, the two parts still communicate over TCP/IP, but unless the ports have been locked down specifically (not recommended, as you'd be unable to run more than one copy), you would have to pass the new port that the database has been exposed as to the application, so that it could communicate with Mongo. This is again, something that Linking can help with.
For a simpler, small installation, where all the dependencies are going in the same container, having both the database and Python runtime started by the program that is initially called as the ENTRYPOINT is also possible. This can be as simple as a shell script, or some other process controller - Supervisord is quite popular, and a number of examples exist in the public Dockerfiles.
Docker provides a couple of examples on how to do it. The lightweight option is to:
Put all of your commands in a wrapper script, complete with testing
and debugging information. Run the wrapper script as your CMD. This is
a very naive example. First, the wrapper script:
#!/bin/bash
# Start the first process
./my_first_process -D
status=$?
if [ $status -ne 0 ]; then
echo "Failed to start my_first_process: $status"
exit $status
fi
# Start the second process
./my_second_process -D
status=$?
if [ $status -ne 0 ]; then
echo "Failed to start my_second_process: $status"
exit $status
fi
# Naive check runs checks once a minute to see if either of the processes exited.
# This illustrates part of the heavy lifting you need to do if you want to run
# more than one service in a container. The container will exit with an error
# if it detects that either of the processes has exited.
# Otherwise it will loop forever, waking up every 60 seconds
while /bin/true; do
ps aux |grep my_first_process |grep -q -v grep
PROCESS_1_STATUS=$?
ps aux |grep my_second_process |grep -q -v grep
PROCESS_2_STATUS=$?
# If the greps above find anything, they will exit with 0 status
# If they are not both 0, then something is wrong
if [ $PROCESS_1_STATUS -ne 0 -o $PROCESS_2_STATUS -ne 0 ]; then
echo "One of the processes has already exited."
exit -1
fi
sleep 60
done
Next, the Dockerfile:
FROM ubuntu:latest
COPY my_first_process my_first_process
COPY my_second_process my_second_process
COPY my_wrapper_script.sh my_wrapper_script.sh
CMD ./my_wrapper_script.sh
I agree with the other answers that using two containers is preferable, but if you have your heart set on bunding multiple services in a single container you can use something like supervisord.
in Hipache for instance, the included Dockerfile runs supervisord, and the file supervisord.conf specifies for both hipache and redis-server to be run.
If a dedicated script seems like too much overhead, you can spawn separate processes explicitly with sh -c. For example:
CMD sh -c 'mini_httpd -C /my/config -D &' \
&& ./content_computing_loop
In docker, there are two ways you can run a program
CMD
ENTRYPOINT
If you want to know the difference between them, please refer here
In CMD/ENTRYPOINT, there are two formats to run a command
SHELL format
EXEC format
SHELL format:
CMD executable_first arg1; executable_second arg1 arg2
ENTRYPOINT executable_first arg1; executable_second arg1 arg2
This version will create a shell and executes above command. Here you can use any shell syntax such as ";", "&", "|", etc. So you can run any number of commands here. If you have complex set of commands to run, you can create separate shell script and use it.
CMD my_script.sh arg1
ENTRYPOINT my_script.sh arg1
EXEC format:
CMD ["executable", "parameter 1", "parameter 2", …]
ENTRYPOINT ["executable", "parameter 1", "parameter 2", …]
Here you can notice that only first parameter is an executable. From the second parameter, everything become an arguments/parameters for that executable.
To run multiple commands in EXEC format
CMD ["/bin/sh", "-c", "executable_first arg1; executable_second"]
CMD ["/bin/sh", "-c", "executable_first arg1; executable_second"]
In above command, we have used shell command as executable to run the command. This is the only way to run multiple commands in EXEC format.
Following are WRONG
CMD ["executable_first parameter", "executable_second parameter"]
ENTRYPOINT ["executable_first parameter", "executable_second parameter"]
CMD ["executable_first", "parameter", ";", "executable_second", "parameter"]
ENTRYPOINT ["executable_first", "parameter", ";", "executable_second", "parameter"]
Can I run multiple programs in a Docker container?
Yes. But with significant risks.
Below is the same answer as above. But with details and a recommended resolution. If you're interested in those.
Not Recommended
Warning. Using the same container for multiple services is not recommended by the Docker community, though. The Docker documentation reads: "It is generally recommended that you separate areas of concern by using one service per container." Source at:
• https://archive.ph/3Roa6#selection-307.2-307.100
• https://docs.docker.com/config/containers/multi-service_container/
If you choose to ignore the recommendation above, you container risk to be with weaker security, increasingly unstable, and in the future a painful growth.
If you are ok with those risks above, the documentation to use one container for multiple services is at:
• https://archive.ph/3Roa6#selection-335.0-691.1
• https://docs.docker.com/config/containers/multi-service_container/
Recommended
If you need a container(s) with stronger security, and more stability, and in the future, scale bigger, as well as better performance, then the Docker community recommends those two steps:
Use one service per Docker container. The end result is that you will have multiple containers.
Use this Docker "Networking" feature to connect any of those containers to your liking.
What I want to do is to make a web app that lists in one single view the version of every application deployed in our Openshift (a fast view of versions). At this moment, the only way I have seen to locate the version of an app deployed in a pod is the ARTIFACT_URL parameter in the envirorment view, that's why I ask for that parameter, but if there's another way to get a pod and the version of its current app deployed, I'm also open to that option as long as I can get it through an API. Maybe I'd eventually also need an endpoint that retrieves the list of the current pods.
I've looked into the Openshift API and the only thing I've found that may help me is this GET but if the parameter :id is what I think, it changes with every deploy, so I would need to be modifying it constantly and that's not practical. Obviously, I'd also need an endpoint to get the list of IDs or whatever that let me identify the pod when I ask for the ARTIFACT_URL
Thanks!
There is a way to do that. See https://docs.openshift.com/enterprise/3.0/dev_guide/environment_variables.html
List Environment Variables
To list environment variables in pods or pod templates:
$ oc env <object-selection> --list [<common-options>]
This example lists all environment variables for pod p1:
$ oc env pod/p1 --list
I suggest redesigning builds and deployments if you don't have persistent app versioning information outside of Openshift.
If app versions need to be obtained from running pods (e.g. with oc rsh or oc env as suggested elsewhere), then you have a serious reproducibility problem. Git should be used for app versioning, and all app builds and deployments, even in dev and test environments should be fully automated.
Within Openshift you can achieve full automation with Webhook Triggers in your Build Configs and Image Change Triggers in your Deployment Configs.
Outside of Openshift, this can be done at no extra cost using Jenkins (which can even be run in a container if you have persistent storage available to preserve its settings).
As a quick workaround you may also consider:
oc describe pods | grep ARTIFACT_URL
to get the list of values of your environment variable (here: ARTIFACT_URL) from all pods.
The corresponding list of pod names can be obtained either simply using 'oc get pods' or a second call to oc describe:
oc describe pods | grep "Name: "
(notice the 8 spaces needed to filter out other Names:)
I need to do the following
Change environment variables according to the published env. Set Set up cron jobs according to the dev. I I would like to run just 1 command line "eb deploy dev" or something similar.
Use setenv
You can set environment variables with setenv. These will then be remembered for that environment.
More details: https://docs.aws.amazon.com/elasticbeanstalk/latest/dg/eb3-setenv.html
Example
For example, suppose you have created an EB environment called 'staging' and you want to set the variable DB to 'localhost', you can use:
eb setenv DB=localhost -e staging
Crons
Now that you have a different environment variables, you can check them in a script etc. to decide if the cron should be set up.
Note that the crons may not actually have access to your environment variables so you need to set those again for the cron while setting up the cron.
This is my solution to the problem, it took some time to setup but now i can do all the changes with 1 command line.
Make your own folder with all the files for all the environments.
In .ebextensions folder setup empty config files for eb.
npm runs a script named "deploy.js" together with the flag of the specific env.
The script will do the following
copy the requested env data to the empty files according to the env
git stash the changes of .ebextensions folder (eb deploys using git)
eb use env
eb deploy
So now i can tun npm run deploy:dev and everything runs
I am a little confused about start up scripts and the command line options. I am building a small raspberry pi based server for my node applications. In order to provide maximum protection against power failures and flash write corruption, the root file system is read only, and that embraces the home directory of my main user, were the production versions of my apps (two of them) are stored. Because the .pm2 directory here is no good for logs etc I currently set PM2_HOME environment variable to a place in /var (which has 512kb unused space around it to ensure writes to i. The eco-system.json file reads this environment variable also to determine where to place its logs.
In case I need to, I also have a secondary user with a read write home directory in another (protected by buffer space around it) partition. This contains development versions of my application code which because of the convenience of setting environments up etc I also want to monitor with PM2. If I need to investigate a problem I can log in to that user and run and test the application there.
Since this is a headless box, and with watchdog and kernel panic restarts built in, I want pm2 to start during boot and at minimum restart the two production apps. Ideally it should also starts the two development versions of the app also but I can live without that if its impossible.
I can switch the read only root partition to read/write - indeed it does so automatically when I ssh into my production user account. It switches back to read only automatically when I log out.
So I went to this account to try and create a startup script. It then said (unsurprisingly) that I had to run a sudo command like so:-
sudo su -c "env PATH=$PATH:/usr/local/bin pm2 startup ubuntu -u pi --hp /home/pi"
The key issue for me here is the --hp switch. I went searching for some clue as to what it means. Its clearly a home directory, but it doesn't match PM2_HOME - which is set to /var/pas in my case to take it out of the read only area. I don't want to try and and spray my home directory with files that shouldn't be there. So am asking for some guidance here
I found out by experiment what it does with an "ubuntu" start up script. It uses it to set PM2_HOME in the script by appending "/.pm2" to it.
However there is nothing stopping you editing the script once it has created it and setting PM2_HOME to whatever you want.
So effectively its a helper for the script, but only that and nothing more special.
I'm using the mysql image as an example, but the question is generic.
The password used to launch mysqld in docker is not visible in docker ps however it's visible in docker inspect:
sudo docker run --name mysql-5.7.7 -e MYSQL_ROOT_PASSWORD=12345 -d mysql:5.7.7
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
b98afde2fab7 mysql:5.7.7 "/entrypoint.sh mysq 6 seconds ago Up 5 seconds 3306/tcp mysql-5.7.7
sudo docker inspect b98afde2fab75ca433c46ba504759c4826fa7ffcbe09c44307c0538007499e2a
"Env": [
"MYSQL_ROOT_PASSWORD=12345",
"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
"MYSQL_MAJOR=5.7",
"MYSQL_VERSION=5.7.7-rc"
]
Is there a way to hide/obfuscate environment parameters passed when launching containers. Alternatively, is it possible to pass sensitive parameters by reference to a file?
Weirdly, I'm just writing an article on this.
I would advise against using environment variables to store secrets, mainly for the reasons Diogo Monica outlines here; they are visible in too many places (linked containers, docker inspect, child processes) and are likely to end up in debug info and issue reports. I don't think using an environment variable file will help mitigate any of these issues, although it would stop values getting saved to your shell history.
Instead, you can pass in your secret in a volume e.g:
$ docker run -v $(pwd)/my-secret-file:/secret-file ....
If you really want to use an environment variable, you could pass it in as a script to be sourced, which would at least hide it from inspect and linked containers (e.g. CMD source /secret-file && /run-my-app).
The main drawback with using a volume is that you run the risk of accidentally checking the file into version control.
A better, but more complicated solution is to get it from a key-value store such as etcd (with crypt), keywhiz or vault.
You say "Alternatively, is it possible to pass sensitive parameters by reference to a file?", extract from the doc http://docs.docker.com/reference/commandline/run/ --env-file=[] Read in a file of environment variables.