Can I run multiple programs in a Docker container

Question

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

User · Answer

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

User · Answer

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

User · Answer

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  amp       amp  amp    content computing loop

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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] Can I run multiple programs in a Docker container?

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