# Runner In the context of **CI/CD (Continuous Integration/Continuous Delivery/Deployment)**, a **runner** is an agent or a lightweight application that executes the jobs defined in a CI/CD pipeline. It is responsible for actually running the commands, scripts, or tasks associated with each job on a machine or within a container. ## Key Features of a Runner: 1. **Execution Environment:** - The runner provides the environment where jobs are executed. This environment can be a physical machine, a virtual machine, a container, or a serverless environment. - It includes the necessary dependencies, tools, and configurations required to run the jobs. 2. **Isolation:** - Runners can be configured to run jobs in isolated environments, such as in Docker containers, to ensure that jobs do not interfere with one another and to maintain consistency across different runs. 3. **Scalability:** - Multiple runners can be used in parallel to execute jobs concurrently, allowing pipelines to scale and handle multiple jobs at the same time. - Runners can be distributed across different machines or cloud environments, enabling horizontal scaling. 4. **Flexibility:** - Runners can be configured to run specific types of jobs based on their capabilities. For example, a runner might be set up specifically to run jobs that require certain software versions or specialized hardware. - They can be tagged with labels to indicate their purpose or capabilities, and jobs can be targeted to specific runners based on these tags. 5. **Self-Hosted vs. Managed:** - **Self-Hosted Runners:** Organizations can host their own runners on their infrastructure, giving them control over the environment, software, and security. - **Managed Runners:** Some CI/CD platforms (like GitHub Actions, GitLab CI, CircleCI, etc.) offer managed runners, which are maintained and hosted by the service provider, reducing the need for infrastructure management. ## How Runners Work in a CI/CD Pipeline: 1. **Job Assignment:** When a pipeline is triggered, the CI/CD system assigns jobs to available runners based on criteria like runner tags, job requirements, and resource availability. 2. **Job Execution:** The runner pulls the necessary code, dependencies, and scripts from the repository, executes the job commands, and generates output (e.g., logs, artifacts). 3. **Result Reporting:** After the job completes, the runner reports the results (success, failure, logs, etc.) back to the CI/CD system, which then decides the next steps in the pipeline. 4. **Resource Cleanup:** Depending on the configuration, the runner may clean up resources (like temporary files, Docker containers) after the job completes to ensure the environment is ready for the next job. ## Example Usage: - **GitLab Runner:** In GitLab CI, a GitLab Runner is used to run jobs in pipelines. It can be installed on any machine, configured to connect to a GitLab instance, and can run jobs either in a shell, in Docker containers, or in other environments like Kubernetes. - **GitHub Actions Runner:** In GitHub Actions, a runner is used to execute workflows. GitHub provides both hosted runners with pre-installed software and the ability to set up self-hosted runners. In summary, a **runner** is the workhorse of a CI/CD system, responsible for executing the jobs defined in a pipeline. It provides the environment and resources needed to run these jobs and plays a critical role in ensuring that the pipeline runs efficiently and reliably. # Names The concept of a **runner** is present in different CI/CD tools, but they often go by different names or have slightly different implementations depending on the platform. Here’s the equivalent of a runner in Jenkins, GitHub Actions, and CircleCI: ## 1. **Jenkins:** - **Equivalent:** **Agent** - **Description:** In Jenkins, an **Agent** (sometimes referred to as a "node" or "slave") is the equivalent of a runner. Agents are machines that Jenkins uses to execute pipeline jobs. The Jenkins master (or controller) assigns jobs to agents based on availability and configuration. Agents can run on physical machines, virtual machines, or even Docker containers, and they are responsible for performing the build, test, or deployment tasks defined in the Jenkins pipeline. - **Configuration:** Agents can be configured in various ways, including static (dedicated machines) or dynamic (using tools like Kubernetes to spin up agents on demand). ## 2. **GitHub Actions:** - **Equivalent:** **Runner** - **Description:** In GitHub Actions, the term **Runner** is used directly. GitHub provides **GitHub-hosted runners** that are managed by GitHub and come pre-installed with popular software tools. Additionally, you can set up **self-hosted runners** on your own infrastructure if you need more control over the environment or need specialized software or hardware. - **Configuration:** Runners are associated with repositories or organizations, and jobs in GitHub Actions workflows are executed on these runners. ## 3. **CircleCI:** - **Equivalent:** **Executor** - **Description:** In CircleCI, the equivalent of a runner is an **Executor**. An Executor defines the environment in which your jobs run, including the type of machine or container, the operating system, and the tools available. CircleCI provides different types of executors such as Docker, machine, macOS, and Windows. - **Configuration:** Executors are configured within the CircleCI configuration file (`.circleci/config.yml`). You can specify Docker images for Docker executors, or use specific machine types for machine executors. ## Summary: - **Jenkins:** **Agent** - **GitHub Actions:** **Runner** - **CircleCI:** **Executor** Each of these terms represents the same basic concept of an environment or agent that executes the jobs defined in your CI/CD pipeline, but the specific name and configuration details vary across platforms. --- Bibliography: - [Title - website.com](need%20bibliography.md)