This project is an example on how to use GitLab's "Managed Terraform State" feature.
Due to personal preferences, I use Docker, docker-compose and Makefiles to execute Terraform files. Docker allows to have an equal execution environment on every machine that executes the code and docker-compose enables mounting the local file system to the Docker container without any hassle.
The Makefile includes all the commands that are needed and allows for sufficient configuration to execute the multiple environments etc.
Follow this guide by GitLab on how to setup your project and permissions. Note down the project ID, which you can find at Settings > General within your project.
Follow this guide by Gitlab on generating your personal access token. Make sure to activate the api scope and note down the generated token (preferrably in your password manager of choice).
The Makefile in this project is based on environment variables, which are loaded through a gitlab.env file, which is excluded from version control through the .gitignore file. I have put a gitlab.env.sample file in the project, which you can either just rename or copy & rename to gitlab.env.
It includes three environment variables: GITLAB_USER_NAME, GITLAB_ACCESS_TOKEN and GITLAB_PROJECT_ID. The user name is simply your email for signing in to GitLab and the other two environment variables can be filled with the information obtained in the previous steps.
Just like with the gitlab.env file, I have put a secret.tfvars.sample file into the project, which you can simply rename to secret.tfvars. The resulting file is again excluded from version control through .gitignore.
The secret.tfvars file is loaded during terraform plan and terraform apply steps by the Makefile.
Now it is your turn to fill the project with your coded infrastructure. I have prepared a production folder with a basic main.tf file in it (the backend declaration must remain so that Terraform can do its state magic on GitLab).
You can create other environments besides production. Just create a folder next to the production folder and place a main.tf file in it with the same backend declaration.
I will show you how to plan/apply the different environments in the next step.
As already stated, this project is based on this central Makefile, which holds all important commands.
If you have Docker and docker-compose installed, you can simply run the commands from it without any modifications. The main commands are make init-{environment}, make plan-{environment} and make apply-{environment}. Replace the {environment} placeholder with the environment you want to run the command for, e.g. make init-production.
If you want to run the code without docker-compose on your host OS, then simply replace the docker-compose run $(docker_compose_service_name) parts in the Makefile with terraform.