Local Development with Tilt

Tilt watches your source files and automatically rebuilds and redeploys affected Prow components when you save a change. This eliminates the manual hack/dev-env.sh -rebuild=hook step and gives you a live view of component status and logs in one terminal.

This guide assumes you have already read Local Development Environment and have the kind cluster running.

Prerequisites

Install Tilt in addition to the tools listed in the Local Development Environment prerequisites.

Workflow

First-time setup

# Create the kind cluster and deploy the core components (one-time).
make dev

This builds all core images and deploys them. Once make dev completes, start Tilt:

tilt up
# or:
make dev-tilt

Tilt opens a browser UI at http://localhost:10350/ showing each component’s build status and live logs.

Day-to-day development

After the first-time setup, start the loop with make dev-tilt. Tilt detects the running cluster and connects immediately - no rebuild needed unless source has changed since the last run.

make dev-tilt

make dev-tilt checks that the kind cluster is running and that tilt is installed before invoking tilt up, giving a clear error if either is missing.

Edit → save → done. Tilt detects the changed file, rebuilds only the affected image (via hack/tilt-build.sh), and rolls out the new pod. For a typical single-component change this takes the same time as a manual hack/dev-env.sh -rebuild=hook, but happens automatically.

Config file changes

Changes to Prow config files (config.yaml, plugins.yaml, or files under jobs/) are applied automatically by the prow-config resource in Tilt. There is no kubectl apply needed.

Stopping Tilt

Press Ctrl+C in the terminal where tilt up is running, or run:

tilt down

tilt down deletes only the resources Tilt manages. Since the Tiltfile does not apply any Kubernetes resources directly (it relies on make dev for initial deployment), tilt down is effectively a no-op for cluster state - the components remain running. Use make dev-teardown to remove the cluster entirely.

How it works

The Tiltfile at the repository root defines:

• prow-config - a local_resource that runs hack/tilt-apply-config.sh whenever config.yaml, plugins.yaml, or the jobs/ directory changes.

• custom_build per component - tells Tilt which source directories to watch and which script to run for each image. When a watched file changes, Tilt calls hack/tilt-build.sh <name> $EXPECTED_REF, which builds the image via prowimagebuilder (wrapping ko) and pushes it to the local registry. Tilt then patches the running Deployment to use the new image tag, triggering a rolling update.

Tilt discovers which Deployments to update by watching the cluster for pods whose image name matches localhost:5001/<component>. No k8s_yaml is needed in the Tiltfile because make dev has already deployed the components.

Customizing with tilt-settings.yaml

The tilt-settings.yaml file at the repository root is git-ignored and lets you override defaults without touching the committed Tiltfile. Copy the checked-in version as a starting point:

cp tilt-settings.yaml tilt-settings.yaml  # already there; just edit it

Disable automatic rebuilds

If pkg/ changes trigger too many simultaneous rebuilds, switch to manual mode. Tilt will only rebuild when you press the ▶ button in its UI:

trigger_mode: manual

Watch additional components

To also watch non-core components (requires them to already be deployed, e.g. via make dev-full):

extra_components:
  - tide
  - gerrit
  - fakegerritserver

Personal Tiltfile overrides (tilt.d/)

Drop any *.tiltfile file into the tilt.d/ directory for local customizations that are never committed. The Tiltfile loads all files from that directory automatically. For example, to narrow the watch paths for hook:

# tilt.d/narrow-hook-deps.tiltfile
prow_component('hook', ['cmd/hook/', 'pkg/github/', 'pkg/plugins/'])

Files in tilt.d/ are git-ignored. The directory itself (containing only .gitkeep) is committed so the path exists for everyone.