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129 lines
5.0 KiB
Markdown
129 lines
5.0 KiB
Markdown
<!--[metadata]>
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+++
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title = "Frequently Asked Questions"
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description = "Docker Compose FAQ"
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keywords = "documentation, docs, docker, compose, faq"
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[menu.main]
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identifier="faq.compose"
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parent="workw_compose"
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weight=90
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+++
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<![end-metadata]-->
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# Frequently asked questions
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If you don’t see your question here, feel free to drop by `#docker-compose` on
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freenode IRC and ask the community.
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## Can I control service startup order?
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Yes - see [Controlling startup order](startup-order.md).
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## Why do my services take 10 seconds to recreate or stop?
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Compose stop attempts to stop a container by sending a `SIGTERM`. It then waits
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for a [default timeout of 10 seconds](./reference/stop.md). After the timeout,
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a `SIGKILL` is sent to the container to forcefully kill it. If you
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are waiting for this timeout, it means that your containers aren't shutting down
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when they receive the `SIGTERM` signal.
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There has already been a lot written about this problem of
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[processes handling signals](https://medium.com/@gchudnov/trapping-signals-in-docker-containers-7a57fdda7d86)
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in containers.
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To fix this problem, try the following:
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* Make sure you're using the JSON form of `CMD` and `ENTRYPOINT`
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in your Dockerfile.
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For example use `["program", "arg1", "arg2"]` not `"program arg1 arg2"`.
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Using the string form causes Docker to run your process using `bash` which
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doesn't handle signals properly. Compose always uses the JSON form, so don't
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worry if you override the command or entrypoint in your Compose file.
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* If you are able, modify the application that you're running to
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add an explicit signal handler for `SIGTERM`.
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* Set the `stop_signal` to a signal which the application knows how to handle:
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web:
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build: .
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stop_signal: SIGINT
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* If you can't modify the application, wrap the application in a lightweight init
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system (like [s6](http://skarnet.org/software/s6/)) or a signal proxy (like
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[dumb-init](https://github.com/Yelp/dumb-init) or
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[tini](https://github.com/krallin/tini)). Either of these wrappers take care of
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handling `SIGTERM` properly.
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## How do I run multiple copies of a Compose file on the same host?
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Compose uses the project name to create unique identifiers for all of a
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project's containers and other resources. To run multiple copies of a project,
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set a custom project name using the [`-p` command line
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option](./reference/overview.md) or the [`COMPOSE_PROJECT_NAME`
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environment variable](./reference/envvars.md#compose-project-name).
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## What's the difference between `up`, `run`, and `start`?
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Typically, you want `docker-compose up`. Use `up` to start or restart all the
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services defined in a `docker-compose.yml`. In the default "attached"
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mode, you'll see all the logs from all the containers. In "detached" mode (`-d`),
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Compose exits after starting the containers, but the containers continue to run
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in the background.
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The `docker-compose run` command is for running "one-off" or "adhoc" tasks. It
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requires the service name you want to run and only starts containers for services
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that the running service depends on. Use `run` to run tests or perform
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an administrative task such as removing or adding data to a data volume
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container. The `run` command acts like `docker run -ti` in that it opens an
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interactive terminal to the container and returns an exit status matching the
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exit status of the process in the container.
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The `docker-compose start` command is useful only to restart containers
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that were previously created, but were stopped. It never creates new
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containers.
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## Can I use json instead of yaml for my Compose file?
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Yes. [Yaml is a superset of json](http://stackoverflow.com/a/1729545/444646) so
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any JSON file should be valid Yaml. To use a JSON file with Compose,
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specify the filename to use, for example:
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```bash
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docker-compose -f docker-compose.json up
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```
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## Should I include my code with `COPY`/`ADD` or a volume?
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You can add your code to the image using `COPY` or `ADD` directive in a
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`Dockerfile`. This is useful if you need to relocate your code along with the
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Docker image, for example when you're sending code to another environment
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(production, CI, etc).
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You should use a `volume` if you want to make changes to your code and see them
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reflected immediately, for example when you're developing code and your server
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supports hot code reloading or live-reload.
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There may be cases where you'll want to use both. You can have the image
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include the code using a `COPY`, and use a `volume` in your Compose file to
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include the code from the host during development. The volume overrides
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the directory contents of the image.
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## Where can I find example compose files?
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There are [many examples of Compose files on
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github](https://github.com/search?q=in%3Apath+docker-compose.yml+extension%3Ayml&type=Code).
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## Compose documentation
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- [Installing Compose](install.md)
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- [Get started with Django](django.md)
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- [Get started with Rails](rails.md)
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- [Get started with WordPress](wordpress.md)
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- [Command line reference](./reference/index.md)
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- [Compose file reference](compose-file.md)
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