How to pass environment variables to Docker containers – Guide
Environment variables are a set of key-value pairs that can be set in the operating system or on the command line of a program. They are commonly used to store information about the current environment, such as the name of the user, the hostname, or the path to a file. Docker containers use environment variables to pass information between themselves and with their host. For example, if you want to run a container that uses a particular version of Python, you can set an environment variable called PYTHONPATH in your container’s configuration file. When your container starts up, Docker will look for this environment variable and use it to find the Python installation files. This feature is really helpful when you want to develop multiple containers that use different versions of Python without having to rebuild each one every time. ..
Environment variables are named values that can be stored and used globally. This is an easy way to store a value in a centralized location (usually in memory) and use it across services, applications, or scripts. To learn more about environment variables, see “Linux 101: What are environment variables?” ..
These variables can be incredibly useful if you’re a container developer. By using them, you can make your job a little easier.
what will you need
To pass environment variables to Docker containers, you need a running Docker instance and a user who is part of the docker group. That’s all you need. Let’s pass some variables.
How to set an environment variable
To pass an environment variable to a container, you first need to set it. I will demonstrate this on Linux. If you use a different operating system for container development, you will need to find out how to do the same on the platform of your choice. ..
SET DB_USER= TechRepublic;
TechRepublic is a technology media company. It has a database of users. ..
echo $VARIABLE No such variable. ..
export PWD=/Users/username/Desktop Now you can access your Desktop from any computer with the following command: cd /Users/username/Desktop
export DB_PWORD = “T3chR3public”
How to pass the variable to a container
To pass an environment variable to a container, you can use the -e flag when running the docker command. For example, to set the PORT environment variable for a container running on port 80, you would run: docker -e PORT=80 mycontainer You can also set environment variables in an .env file. To do this, create a new file called .env and add the following lines: PORT=80 PORT_CONTAINER=mycontainer ..
docker run -v " $HOME /.git" : " $HOME /.git/config" This is because the variables in the .git directory are not accessible to the container.
docker run –name postgresql -e $ DB_PWORD -e $ DB_USER -d postgres –name=postgresql-9.4
export DB_PWORD=‘dbpassword’ export DB_USER=‘dbuser’ If you try to deploy the container as such, it will run but exit immediately. Why? Because unlike the Linux system, where you can set environment variables as you like, container images expect certain variables. For example, PostgreSQL database cannot use DB_PWORD or DB_USER as it expects POSTGRES_PASSWORD and POSTGRES_USER. To do this, you can set these environment variables on your Linux hosts with the commands:
To set a password for your PostgreSQL database: export POSTGRES_PASSWORD = t3chr3public ..
export POSTGRES_USER = TechRepublic
grep -v ‘^#’ /etc/passwd This will grep through the contents of the /etc/passwd file, looking for any matches that start with #.
docker run –name postgresql -e POSTGRES_PASSWORD -e POSTGRES_USER -d postgres –name=postgres
psql -U postgres -d postgres The command will succeed and the container will remain running. You can test it by accessing the PostgreSQL command inside the container, issuing: ..
To connect to a PostgreSQL server running inside a Docker container, use the following command: ..
You should find yourself on the PostgreSQL console in your container.
How to pass variables with an .env file
One of the problems with passing environment variables as described above is that they remain in memory (unless you unset them). To avoid this, we use an environment variable file.
VIRTUAL_ENV= “production” This will create a new environment variable called VIRTUAL_ENV that points to the production environment.
In this file, paste the following: In this file, paste the following: In this file, paste the following:
Save the file and close it.
passwd This will ask the system for the user’s password and store it in a file.
docker run –name postgresql –env-file .env -d postgres:latest ..
docker run -d –name postgres -p 5432:5432 -p 9600:9600 postgres This will launch a PostgreSQL container that is accessible at http://localhost:5432/. You can also access it from the command line with the following command: docker exec -it postgres /usr/bin/pgsql
docker exec -it postgresql psql -U TechRepublic -p 9200
To pass environment variables to a Docker container, you can use either the command line or an .env file. This method is helpful for developers because it makes things a little more efficient. ..
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Final note
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