Continuous Integration

Tempo ships reusable GitHub Actions workflows so your project can build, package, run, test and release without writing pipeline code from scratch.

They live in .github/workflows. TempoSample's tempo_sample_build_and_package.yml is a good reference for calling them.

Workflow	Purpose
build_and_package.yml	Build, package, and optionally release your Tempo project.
test_packaged.yml	Run client API tests against a packaged artifact. Language-agnostic and reusable.
publish_engine_mods.yml	Publish a pre-modded Unreal image to your private GHCR.
prune_engine_mods.yml	Keep only recent engine-mod image tags.

Prerequisites

You'll need EPIC_DOCKER_USERNAME and EPIC_DOCKER_TOKEN secrets configured, to pull Epic's base Unreal image.

Speeding up builds with a pre-modded engine image

Tempo modifies the Unreal engine in place via patches in EngineMods/. By default build_and_package.yml applies these inside each CI run, which adds ~10–15 minutes and consumes the GitHub Actions cache budget — 10 GB on the free tier, shared with the per-commit build cache.

For larger projects you can opt into a pre-modded Unreal image hosted on your own private GHCR, which the build workflow pulls instead of re-applying mods every run.

1. Add a publish workflow

.github/workflows/publish_engine_mods.yml

name: Publish Pre-Modded Engine Image
on:
  push:
    branches: [main]
    paths:
      - 'Plugins/Tempo/EngineMods/**'
      - 'Plugins/Tempo/Dockerfile'
      - 'Plugins/Tempo/Scripts/InstallEngineMods.sh'
  workflow_dispatch:
jobs:
  publish:
    permissions:
      contents: read
      packages: write
    strategy:
      matrix:
        unreal_version: ["5.7", "5.8"]
      fail-fast: false
    uses: tempo-sim/Tempo/.github/workflows/publish_engine_mods.yml@main
    with:
      unreal_version: ${{ matrix.unreal_version }}
      image_name: ghcr.io/${{ github.repository_owner }}/tempo-unreal-modded
      tempo_root: Plugins/Tempo  # adjust to your Tempo submodule path
    secrets: inherit
  prune:
    needs: publish
    permissions:
      packages: write
    uses: tempo-sim/Tempo/.github/workflows/prune_engine_mods.yml@main
    with:
      package_name: tempo-unreal-modded
      package_owner: ${{ github.repository_owner }}
    secrets: inherit

2. Point your build workflow at it

Pass engine_mods_image: ghcr.io/<your-org>/tempo-unreal-modded to your existing build_and_package.yml caller, and grant it packages: read.

The build workflow computes the EngineMods hash, attempts a docker pull of the matching tag, and skips the in-workflow engine-mods install when the pull succeeds. If the pull fails for any reason — image not yet published for the current hash, permissions misconfigured — the workflow falls back to the in-workflow path. There is no breakage, just no speedup.

Setup notes

• Run your new publish_engine_mods workflow manually once via workflow_dispatch before merging the engine_mods_image change to your build workflow, so the first image exists when the build runs.
• The published image contains UE-derived content, which the Unreal Engine EULA does not permit redistributing publicly. Your org's GHCR package-creation policy must be set to "Private" (under Settings → Packages in the org admin), and the package will inherit private visibility on first push. If your org's policy allows public, flip the package to private via its settings page after the first push.
• The prune job keeps only the most recent tag per Unreal version, which is enough since EngineMods rarely change. Pass keep: 3 (or higher) for a longer history.

Running the test suites

tempo_build_and_package.yml builds and packages once, uploads the artifact, then fans out to the reusable test_packaged.yml — parallel jobs per (Unreal version × test group), across both the Python and Rust clients. Each job downloads the same artifact, so the expensive build runs once while tests run in parallel.

Testing

Things that only bite in CI

Clean builds are slow

A fully clean CI run takes about two hours. Cache entries expire after a configurable retention period (GitHub's default is 7 days; set it per repository under Settings → Actions → General), and are also evicted once the repository exceeds its cache size limit. Either way, any fix has to work from a cold start — a change that only works incrementally will eventually meet a run with nothing cached.

Cold packages need -skipiostore

A clean CI package can crash because iostore cannot find engine content under Saved/Temp. Pass -skipiostore in CI.