Title: Ephemeral runners for GitHub Actions: just-in-time, single-use · Codemany docs
URL: https://codemany.com/docs/guides/ephemeral-runners
Description: Ephemeral runners for GitHub Actions on your own Mac or Linux: Codemany registers a just-in-time runner per job, runs one job, wipes it and starts a fresh one.
All pages as Markdown: https://codemany.com/llms.txt

---

[Guides](https://codemany.com/docs#guides)

# Ephemeral (single-use, just-in-time) self-hosted runners for GitHub Actions

A fresh runner for every job, recycled after.

An ephemeral runner takes one job and then goes away, so no job starts with another job's runner or work folder. Codemany gives every GitHub Actions job a fresh single-use runner on your own Mac or Linux machine. Each one registers with GitHub just in time, takes one job and exits; its folder is wiped and a fresh runner starts.

## Why one runner per job

A long-lived self-hosted runner keeps its folder from job to job. Files a build left behind can break or change the next build. With GitHub's runner on its own, that cleanup between jobs is yours, along with updates and scaling ([Codemany compared](https://codemany.com/docs/compare)).

A single-use runner starts every job from the same clean folder. Results don't depend on which job ran before.

## How Codemany's just-in-time runners work

1. Register just in time
   Codemany registers a runner with GitHub just in time, with the labels `self-hosted` and `codemany`, plus the operating system and CPU labels GitHub's runner adds.
2. Take one job
   GitHub still schedules jobs and shows the logs. It hands the runner one job whose `runs-on` labels it has.
3. Exit and wipe
   When the job ends, the runner exits, Codemany removes it, and its folder is wiped.
4. Start a fresh one
   A fresh runner starts. Each repo keeps a warm runner while there are spares; idle runners move to repos with waiting jobs. Busy runners are never touched.

Details: [How Codemany runs jobs](https://codemany.com/docs/advanced#how-it-works).

## Use them in a workflow

You don't write any just-in-time config yourself. Change one line, `runs-on`:

```
name: CI
on: push
jobs:
  build:
    runs-on: [self-hosted, codemany]
    steps:
      - uses: actions/checkout@v4
      - run: make test
```

To send a job to your Linux machines only, use `runs-on: [self-hosted, Linux, codemany]`. More in [Runner labels](https://codemany.com/docs/advanced#labels).

## What is wiped and what carries over

- **Wiped:** the runner and its folder, after every job.
- **Kept:** downloads from `actions/setup-go`, `setup-node`, `setup-python` and other `actions/setup-*` steps, in a shared tool cache at `~/.codemany/toolcache`, pruned past 20 GB ([Tools and caching](https://codemany.com/docs/advanced#tools)).
- **Kept:** the tools installed on your machine. Nothing is preinstalled; jobs get what you have.
- **Not undone:** a job runs as your user, so files it changes outside its folder and programs it leaves running stay. A fresh runner keeps jobs apart from each other, not from your Mac ([What a job can do](https://codemany.com/docs/security#jobs)).

## Crashes, hangs and updates

- A crashed runner is replaced, backing off from 5 seconds up to 5 minutes.
- A runner offline for 2 minutes is stopped, with leftover processes such as simulators, and replaced.
- Updates wait until running jobs finish. GitHub errors and rate limits never stop a running job.

## How many run at once

Each runner budgets 4 GB of memory, 15 GB of disk and 2 performance cores. An 8 GB Mac runs 1 job at a time; a 16 GB Mac runs 3. `codemany capacity` prints how many fit. To run more, [add machines](https://codemany.com/docs/machines).

## Questions

### What is an ephemeral runner in GitHub Actions?

An ephemeral runner takes one job and is then removed, so the next job gets a fresh runner and work folder. Codemany starts one for every job on your own Mac or Linux machine.

### What is a just-in-time runner?

A runner registered with GitHub just in time for one job and removed when that job ends. Every Codemany runner is one, so no runner outlives its job.

### Is an ephemeral runner a sandbox, or more secure?

It is not a sandbox. It keeps jobs apart from each other, so nothing a job leaves in its runner folder reaches the next, but not from your machine. Read [runner security](https://codemany.com/docs/guides/runner-security) before you point it at a repo.

### Do I have to create just-in-time (JIT) configs or remove runners myself?

No. Codemany registers each runner just in time and removes it when the job ends. You only change `runs-on`.

### Does every job start with a cold cache?

Not for `actions/setup-*` downloads: they stay in the shared tool cache. **Pre-warm** fills it with the versions your workflows ask for.

### Where do I see the logs?

On GitHub, as with any runner. Codemany Console also shows runs and job logs, with secrets masked on your machine.

### How do I set up ephemeral runners for GitHub Actions?

Follow [Get started](https://codemany.com/docs/get-started), or the guides for [a runner on a Mac](https://codemany.com/docs/guides/mac-runner) and [a runner on Linux](https://codemany.com/docs/guides/linux-runner).

[Previous Self-hosted runner on Linux](https://codemany.com/docs/guides/linux-runner)[Next Cut GitHub Actions costs](https://codemany.com/docs/guides/actions-cost)