How one can Cross Surroundings Variables to Docker Containers

Applications typically management operation by means of configuration bundled with the software program, and surroundings variables enable customers to set them at runtime. Nevertheless, working processes in Docker containers complicates issues, so how do you go surroundings variables to a container?

What Are Surroundings Variables Used For?

Surroundings variables help you decouple the configuration from the appliance’s executable. For instance, you wouldn’t need to retailer your manufacturing database password in your codebase—if you happen to did, it might be seen from Git, and anybody with entry to your code may take down your database.

As an alternative, you set it with an surroundings variable, which shops a easy key-value pair, and lets you entry the worth in any utility working in the identical shell session (they’re not globally accessible).  This additionally has the good thing about having the ability to simply outline totally different configuration for various environments. For instance, having separate keys for growth and manufacturing databases, or utilizing a distinct API endpoint.

Setting these variables for Docker containers could be performed in three major methods—with CLI arguments, .env config information, or by means of docker-compose.

With a Command Line Argument

The command used to launch Docker containers, docker run, accepts ENV variables as arguments. Merely run it with the -e flag, shorthand for --env, and go in the important thing=worth pair:

sudo docker run 
-e POSTGRES_USER='postgres' 
-e POSTGRES_PASSWORD='password' 

And, if you have already got these surroundings variables set within the surroundings that’s working that command, you possibly can simply go them in instantly by identify:

// set variable

// use it later

Extra Safety With an .env File

Passing variables with CLI arguments works nice, however it has a draw back—these variables are seen from the host. They’re logged within the command historical past, and visual within the course of itemizing for the launched course of.

Linux has a inbuilt technique to handle permissions for this—file entry. Storing the variables in an .env file lets you management entry to that file with file permissions (chmod, chown).

Create an .env file with variables within the following format, every on a brand new line:


Then, go it to docker run with the --env-file flag:

docker run --env-file ./envfile ...

With Docker-Compose

After all, many individuals don’t launch Docker containers instantly with docker run, and as a substitute choose to make use of a docker-compose file to deal with the configuration of a number of containers all representing a single utility.

To go surroundings variables to a container launched this fashion, you’ll have to configure the compose file to go the session’s variables by means of to the Docker container. This configuration right here passes the POSTGRES_USER variable to each the construct surroundings and the runtime surroundings, and units a default worth if it doesn’t exist.

model: '3.1'
      context: .
        - POSTGRES_USER=${POSTGRES_USER:-default}

You’ll need to set the surroundings variables earlier than working docker-compose up, in any other case it will be unable to entry them. You might retailer them within the compose file, however that’s normally tracked and versioned, which defeats the aim of env variables.

With Kubernetes

Kubernetes is an orchestration system that may deal with working a whole bunch of containers throughout a community. It nonetheless makes use of Docker, however you’ll solely ever contact configuration, so passing surroundings variables instantly received’t work.

As an alternative, you possibly can outline them within the configuration for the Pod:

apiVersion: v1
variety: Pod
  identify: instance
    - ...
        - identify: SERVICE_PORT
          worth: "80"
        - identify: SERVICE_IP
          worth: ""

Kubernetes is difficult, and there are a number of other ways to work with surroundings variables. To be taught extra, you possibly can learn their guides on injecting information into Pods.

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