Gitlab¶

Runner¶

Definition: Docker is a platform that allows developers to package applications into lightweight, portable containers. These containers include all the necessary dependencies, libraries, and configuration files, ensuring consistent behavior across different environments.
Role in GitLab Runner:
When using the Docker executor in GitLab Runner, the runner creates a new Docker container for each job in the CI/CD pipeline.
The job runs inside this container, isolated from the host system and other jobs.
This ensures reproducibility and avoids conflicts between dependencies or configurations.
Key Characteristics:
Directly interacts with the Docker daemon on the host machine.
Requires Docker to be installed on the host where the runner is running.
Suitable for most use cases where you want to run jobs in isolated environments.

Definition: Docker Machine is a tool that simplifies the creation and management of Docker hosts on remote systems (e.g., cloud providers like AWS, Google Cloud, or local virtual machines). It allows you to provision and manage Docker environments remotely.
Role in GitLab Runner:
When using the Docker Machine executor in GitLab Runner, the runner dynamically provisions a new Docker host (a virtual machine) for each job.
The job is then executed on this newly created Docker host.
After the job completes, the Docker host is typically destroyed to clean up resources.
Key Characteristics:
Useful for scenarios where you need to scale horizontally by provisioning additional machines for each job.
Ideal for distributed workloads or when you want to isolate jobs at the machine level rather than just the container level.
Requires more setup, as it involves configuring access to a cloud provider or virtualization platform.

Aspect	Docker Executor	Docker Machine Executor
Isolation Level	Jobs run in isolated Docker containers on the same host.	Jobs run on separate Docker hosts (virtual machines).
Resource Usage	Shares resources with the host machine.	Each job gets its own dedicated machine, consuming more resources.
Setup Complexity	Simple; requires Docker installed on the host.	More complex; requires configuring Docker Machine and access to a cloud provider or VM manager.
Scalability	Limited to the capacity of the host machine.	Highly scalable; can provision additional machines dynamically.
Use Case	Ideal for most standard CI/CD pipelines.	Best for large-scale or distributed workloads requiring high isolation.

Docker Executor:
Use this when you want lightweight, fast execution of jobs within containers on a single host.
Suitable for most projects where resource constraints and isolation requirements are moderate.
Docker Machine Executor:
Use this when you need to dynamically scale your CI/CD infrastructure by provisioning additional machines for each job.
Ideal for large-scale projects or when you require complete isolation between jobs at the machine level.