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3rd chunk of `content/guides/ruby/containerize.md`
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The Dockerfile above assumes you are using Thruster together with Puma as an application server. In case you are using any other server, you can replace the last three lines with the following:

```dockerfile
# Start the application server
EXPOSE 3000
CMD ["./bin/rails", "server"]
```

This Dockerfile uses a script at `./bin/docker-entrypoint` as the container's entrypiont. This script prepares the database and runs the application server. Below is an example of such a script.

```bash {title=docker-entrypoint}
#!/bin/bash -e

# Enable jemalloc for reduced memory usage and latency.
if [ -z "${LD_PRELOAD+x}" ]; then
    LD_PRELOAD=$(find /usr/lib -name libjemalloc.so.2 -print -quit)
    export LD_PRELOAD
fi

# If running the rails server then create or migrate existing database
if [ "${@: -2:1}" == "./bin/rails" ] && [ "${@: -1:1}" == "server" ]; then
  ./bin/rails db:prepare
fi

exec "${@}"
```

Besides the two files above you will also need a `.dockerignore` file. This file is used to exclude files and directories from the context of the build. Below is an example of a `.dockerignore` file.

```text {collapse=true,title=".dockerignore"}
# See https://docs.docker.com/engine/reference/builder/#dockerignore-file for more about ignoring files.

# Ignore git directory.
/.git/
/.gitignore

# Ignore bundler config.
/.bundle

# Ignore all environment files.
/.env*

# Ignore all default key files.
/config/master.key
/config/credentials/*.key

# Ignore all logfiles and tempfiles.
/log/*
/tmp/*
!/log/.keep
!/tmp/.keep

# Ignore pidfiles, but keep the directory.
/tmp/pids/*
!/tmp/pids/.keep

# Ignore storage (uploaded files in development and any SQLite databases).
/storage/*
!/storage/.keep
/tmp/storage/*
!/tmp/storage/.keep

# Ignore assets.
/node_modules/
/app/assets/builds/*
!/app/assets/builds/.keep
/public/assets

# Ignore CI service files.
/.github

# Ignore development files
/.devcontainer

# Ignore Docker-related files
/.dockerignore
/Dockerfile*
```

The last optional file that you may want is the `compose.yaml` file, which is used by Docker Compose to define the services that make up the application. Since SQLite is being used as the database, there is no need to define a separate service for the database. The only service required is the Rails application itself.
Title: Docker Ignore File and Docker Compose Considerations
Summary
This section describes the use of a `.dockerignore` file to exclude unnecessary files and directories (like git data, environment files, logs, temp files, node modules, and development/CI files) from the Docker build context, optimizing the final image size. It also mentions Docker Compose, suggesting that for applications using SQLite, a separate database service isn't needed, and only the Rails application service needs to be defined in the `compose.yaml` file.