Docker Environment Variables
Docker Environment Variables#
Docker Image Built-time Variables#
To set build time variables - use the Dockerfile, these settings are baked into the image.
Args#
Args are to help you not repeat yourself in a Dockerfile
ARG some_variable_name
That tells docker that it should expect some_variable_name to be passed in at build time.
You do that with:
docker build --build-arg some_variable_name=a_value
ARG’s are not available to running containers
Envs#
ENV can be used to define default environment variables
ENV foo /bar
This environment variable is available to containers
You can set a dynamic build time variable, that will be available to the container with:
ARG some_variable_name
ENV env_var_name=$some_variable_name
You can override ENV variables when starting containers with:
docker run -e "env_var_name=another_value" alpine env
Docker Compose#
Environment stuff only applies to containers, not images
You can also specify a file to read values from