Build from a Dockerfile

We will look for and use a Dockerfile at the service's root if it exists.

Railway notifies you when it's using the Dockerfile in the build process with the following message in the logs:

==========================
Using detected Dockerfile!
==========================

Custom Dockerfile Path

By default, we look for a file named Dockerfile in the root directory. If you want to use a custom filename or path, you can set a variable defining the path.

In your service variables, set a variable named RAILWAY_DOCKERFILE_PATH to specify the path to the file.

For example, if your Dockerfile was called Dockerfile.origin, you would specify it like this:

RAILWAY_DOCKERFILE_PATH=Dockerfile.origin

If your Dockerfile is in another directory, specify it like this:

RAILWAY_DOCKERFILE_PATH=/build/Dockerfile

Use Config as Code

You can also set your custom Dockerfile path using config as code.

Using Variables at Build Time

If you need to use the environment variables that Railway injects at build time, which include variables that you define and Railway-provided variables, you must specify them in the Dockerfile using the ARG command.

For example:

# Specify the variable you need
ARG RAILWAY_SERVICE_NAME
# Use the varible
RUN echo $RAILWAY_SERVICE_NAME

Be sure to declare your environment variables in the stage they are required in:

FROM node

ARG RAILWAY_ENVIRONMENT

Cache Mounts

Railway supports cache mounts in your Dockerfile in the following format:

--mount=type=cache,id=s/<service id>-<target path>,target=<target path>

Replace <service id> with the id of the service.

Target Path

Unsure of what your target path should be? Refer to the Nixpacks source code. Within the providers directory, find the file that aligns with your respective language or runtime, and check for the variable that indicates the CACHE_DIR.

Example

As an example, within the python provider definition, you can see the PIP_CACHE_DIR is /root/.cache/pip.

So the mount command is specified like this:

--mount=type=cache,id=s/<service id>-/root/cache/pip,target=/root/.cache/pip

Docker Compose

Railway doesn't support docker compose at the moment.