What is Runner? | DevOps Dictionary

Understanding CI/CD Runners

What Is a Runner in Simple Terms

A runner is the worker that actually runs your pipeline jobs. When GitHub Actions starts a job, it needs somewhere to execute the commands — that somewhere is a runner. Think of runners as the factory workers on your assembly line: the pipeline is the process, the runner is the person (or machine) doing the work.

GitHub-hosted runners are virtual machines that GitHub spins up for each job and terminates when the job completes. Self-hosted runners are machines you manage — physical servers, VMs, or Kubernetes pods — that stay registered with your CI platform and pick up jobs from a queue.

How It Works

◈ DIAGRAM

+------------------------------------------+
| GitHub Actions Workflow                  |
| job: build                               |
| runs-on: ubuntu-latest                   |
+------------------------------------------+
                    |
            job queued
                    |
                    v
+------------------------------------------+
| GitHub picks an available runner         |
|                                          |
| GitHub-hosted:                           |
|   Fresh Ubuntu VM, 2 vCPU, 7GB RAM      |
|   Pre-installed: Node, Python, Docker   |
|   Cost: billed per minute               |
|   Terminated after job completes        |
+------------------------------------------+
          OR
+------------------------------------------+
| Self-hosted:                             |
|   Your server/VM/Kubernetes pod          |
|   Custom tools, faster network,          |
|   access to private resources            |
|   Cost: your infrastructure              |
+------------------------------------------+

Runner selection by label:

YAML

jobs:
  build:
    ## GitHub-hosted runner
    runs-on: ubuntu-latest
 
  deploy-prod:
    ## Self-hosted runner with specific label
    ## Only runs on your runner in the production VPC
    runs-on: [self-hosted, production, linux]
 
  build-arm:
    ## GitHub-hosted ARM runner
    runs-on: ubuntu-latest
    strategy:
      matrix:
        platform: [linux/amd64, linux/arm64]

Self-hosted runner setup:

Bash

## Download runner package
mkdir actions-runner && cd actions-runner
curl -o actions-runner-linux-x64-2.311.0.tar.gz -L \
  https://github.com/actions/runner/releases/download/v2.311.0/actions-runner-linux-x64-2.311.0.tar.gz
tar xzf ./actions-runner-linux-x64-2.311.0.tar.gz
 
## Configure runner (get token from GitHub repo settings)
./config.sh \
  --url https://github.com/razorpay/payment-api \
  --token RUNNER_TOKEN \
  --labels production,linux,payment-vpc
 
## Install as a service
sudo ./svc.sh install
sudo ./svc.sh start
 
## GitLab runner registration
gitlab-runner register \
  --url https://gitlab.com \
  --token REGISTRATION_TOKEN \
  --executor docker \
  --docker-image alpine:latest \
  --description payment-api-runner

Practical Commands

Bash

## GitHub CLI -- list runners for a repository
gh api repos/OWNER/REPO/actions/runners
 
## List runner groups
gh api orgs/ORG/actions/runner-groups
 
## GitLab -- check runner status
gitlab-runner status
gitlab-runner list
 
## Jenkins -- check node status
java -jar jenkins-cli.jar -s http://jenkins.internal list-nodes

Troubleshooting

Symptom	Check	What to Look For
Job queued but not starting	Runner availability	All runners busy or offline
Self-hosted runner offline	Runner service status	`./svc.sh status` on runner machine
Tool not found on runner	Runner image/labels	Use correct runner label for required tools
Runner picking wrong jobs	Label configuration	Labels must match exactly

COMMON MISTAKE / WARNING
**Security:** Never use self-hosted runners on public repositories unless you have implemented strict security controls. A malicious PR can execute arbitrary code on your self-hosted runner — which may have access to production credentials and infrastructure. Use GitHub-hosted runners for public repos and self-hosted only for private repos with restricted access.

REMEMBER THIS
**Remember:** GitHub-hosted runners start fresh every time — nothing persists between jobs. If Job A installs a tool, Job B does not have it. Use setup actions (actions/setup-node, actions/setup-python) at the start of each job, or build a custom runner image with your tools pre-installed.

COMMON MISTAKE / WARNING
**Common Mistake:** Installing tools directly on a self-hosted runner instead of using Docker containers or setup actions. A runner that has been manually configured over time becomes a snowflake — impossible to reproduce, impossible to scale horizontally, and a nightmare when the machine needs to be replaced. Keep runners stateless and install tools per-job using setup actions or Docker.

PLACEMENT PRO TIP
**Tip:** Use runner labels to target specific hardware for specific jobs. A Docker build job that benefits from a high-core-count machine can use `runs-on: [self-hosted, high-cpu]`. An ARM image build runs on `runs-on: [self-hosted, arm64]`. Label your runners by capability, not by machine name, so you can scale horizontally.