Is there any way to make docker-compose start a service without running the declared command?
Not sure if any such option exists, nothing obvious in the flags for docker-compose up. It would be useful for debugging as presently I have to comment out the command in order to enter a container that otherwise exits on startup.
In this case, there's no command in the Dockerfile, but there's a command in docker-compose.yml.
Based on jonrsharpe's comment, the answer is to use run instead as it will start the container.
docker-compose run service bash
This makes it possible to enter the container and debug the problem so the real command can run.
Related
I'm somewhat new to Docker. I would like to be able to use Docker to distribute a CLI program, but run the program normally once it has been installed. To be specific, after running docker build on the system, I need to be able to simply run my-program in the terminal, not docker run my-program. How can I do this?
I tried something with a Makefile which runs docker build -t my-program . and then writes a shell script to ~/.local/bin/ called my-program that runs docker run my-program, but this adds another container every time I run the script.
EDIT: I realize is the expected behavior of docker run, but it does not work for my use-case.
Any help is greatly appreciated!
If you want to keep your script, add the remove flag --rm to the docker run command. The remove flag removes the container automatically after the entry-point process has exit.
Additionally, I would personally prefer an alias for this. Simply add something like this example alias my-program="docker run --rm my-program" to your ~/.bashrc or ~/.zshrc file. This even has the advantage that all other parameters after the alias (my-program param1 param2) are automatically forwarded to the entry-point of your image without any additional effort.
So, is there a point in the command "start"? like in "docker start -i albineContainer".
If I do this, I can't really do anything with the albine inside the container, I would have to do a run and create another container with the "-it" command and "sh" after (or "/bin/bash", don't remember it correctly right now).
Is that how it will go most of the times? delete and rebuilt containers and do the command "-it" if you want to do stuff in them? or would it more depend on the Dockerfile, how you define the cmd.
New to Docker in general and trying to understand the basics on how to use it. Thanks for the help.
Running docker run/exec with -it means you run the docker container and attach an interactive terminal to it.
Note that you can also run docker applications without attaching to them, and they will still run in the background.
Docker allows you to run a program (which can be bash, but does not have to be) in an isolated environment.
For example, try running the jenkins docker image: https://hub.docker.com/_/jenkins.
this will create a container, without you having attach to it, and you would still be able to use it.
You can also attach to an existing, running container by using docker exec -it [container_name] bash.
You can also use docker logs to peek at the stdout of a certain docker container, without actually attaching to its shell interactively.
You almost never use docker start. It's only possible to use it in two unusual circumstances:
If you've created a container with docker create, then docker start will run the process you named there. (But it's much more common to use docker run to do both things together.)
If you've stopped a container with docker stop, docker start will run its process again. (But typically you'll want to docker rm the container once you've stopped it.)
Your question and other comments hint at using an interactive shell in an unmodified Alpine container. Neither is a typical practice. Usually you'll take some complete application and its dependencies and package it into an image, and docker run will run that complete packaged application. Tutorials like Docker's Build and run your image go through this workflow in reasonable detail.
My general day-to-day workflow involves building and testing a program outside of Docker. Once I believe it works, then I run docker build and docker run, and docker rm the container once I'm done. I rarely run docker exec: it is a useful debugging tool but not the standard way to interact with a process. docker start isn't something I really ever run.
I wrote a Dockerfile for a service (I have a CMD pointing to a script that starts the process) but I cannot run any other commands after the process has started? I tried using '&' to run the process in the background so that the other commands would run after the process has started but it's not working? Any idea on how to achieve this?
For example, consider I started a database server and wanted to run some scripts only after the database process has started, how do I do that?
Edit 1:
My specific use case is I am running a Rabbitmq server as a service and I want to create a new user, make him administrator and delete the default guest user once the service starts in a container. I can do it manually by logging into the docker container but I wanted to automate it by appending these to the shell script that starts the rabbitmq service but that's not working.
Any help is appreciated!
Regards
Specifically around your problem with Rabbit MQ - you can create a rabbitmq.config file and copy that over when creating the docker image.
In that file you can specify both a default_user and default_pass that will be created when an the database is set from scratch see https://www.rabbitmq.com/configure.html
AS for the general problem - you can change the entry point to a script that runs whatever you need and the service you want instead of the run script of the service
I partially understood your question. Based on what I perceived from your question, I would recommend you to mention the Copy command to copy the script you want to run into the dockerfile. Once you build an image and run the container, start the db service. Then exec the container and get into the container, run the script manually.
If you have CMD command in the dockerfile, then it will be overwritten by the command you specify during the execution. So, I don't think you have any other option to run the script unless you don't have CMD in the dockerfile.
I'm trying to pull and set a container with an database (mysql) with the following command:
docker-compose up
But for some reason is failing to start the container is showing me this:
some_db exited with code 0
But that doesn't give me any information of why that happened so I can fix it, so how can I see the details of that error?.
Instead of looking for how to find an error in your composition, you should change your process. With docker it is easy to fall into using all of the lovely tools to make things work seamlessly together, but this sounds like an individual container issue, not an issue with docker compse. You should try building an empty container with the baseimage you want then using docker exec -it <somecontainername> sh to go into it and run the commands you're trying to execute in your entrypoint manually to find the specific breakpoint.
Try at least docker logs <exited_container_name/id> (or more recently: docker container logs <exited_container_name/id>)
That way, you can check if there was any error message.
An exited container means the main process stopped: you need to make sure that main process remains up in order for the container to not exit immediately.
Try also docker inspect <exited_container_name/id> (or, again, docker container inspect <exited_container_name/id>)
If you see for instance "OOMKilled": true, that would mean the container memory was exceeded. You can also look for the "ExitCode" for clues.
See more at "Ten tips for debugging Docker containers" from Mark Betz.
Is it possible to add instructions like RUN in Dockerfile that, instead of run on docker build command, execute when a new container is created with docker run? I think this can be useful to initialize a volume attached to host file system.
Take a look at the ENTRYPOINT command. This specifies a command to run when the container starts, regardless of what someone provides as a command on the docker run command line. In fact, it is the job of the ENTRYPOINT script to interpret any command passed to docker run.
I think you are looking for the CMD
https://docs.docker.com/reference/builder/#cmd
The main purpose of a CMD is to provide defaults for an executing
container. These defaults can include an executable, or they can omit
the executable, in which case you must specify an ENTRYPOINT
instruction as well.
Note: don't confuse RUN with CMD. RUN actually runs a command and
commits the result; CMD does not execute anything at build time, but
specifies the intended command for the image.
You should also look into using Data Containers see this excellent Blog post.
Persistent volumes with Docker - Data-only container pattern
http://container42.com/2013/12/16/persistent-volumes-with-docker-container-as-volume-pattern/