Architecture

Prow in a Nutshell

Prow creates jobs based on various types of events, such as:

• GitHub events (e.g., a new PR is created, or is merged, or a person comments “/retest” on a PR),

• Pub/Sub messages,

• time (these are created by Horologium and are called periodic jobs), and

• retesting (triggered by Tide).

Jobs are created inside the Service Cluster as Kubernetes Custom Resources. The Prow Controller Manager takes triggered jobs and schedules them into a build cluster, where they run as Kubernetes pods. Crier then reports the results back to GitHub.

flowchart TD classDef yellow fill:#ff0 classDef cyan fill:#0ff classDef pink fill:#f99 subgraph Service Cluster["<span style='font-size: 40px;'><b>Service Cluster</b></span>"] Deck:::cyan Prowjobs:::yellow Crier:::cyan Tide:::cyan Horologium:::cyan Sinker:::cyan PCM[Prow Controller Manager]:::cyan Hook:::cyan subgraph Hook WebhookHandler["Webhook Handler"] PluginCat(["'cat' plugin"]) PluginTrigger(["'trigger' plugin"]) end end subgraph Build Cluster[<b>Build Cluster</b>] Pods[(Pods)]:::yellow end style Legend fill:#fff,stroke:#000,stroke-width:4px subgraph Legend["<span style='font-size: 20px;'><b>LEGEND</b></span>"] direction LR k8sResource[Kubernetes Resource]:::yellow prowComponent[Prow Component]:::cyan hookPlugin([Hook Plugin]) Other end Prowjobs <-.-> Deck <-----> |Serve| prow.k8s.io GitHub ==> |Webhooks| WebhookHandler WebhookHandler --> |/meow| PluginCat WebhookHandler --> |/retest| PluginTrigger Prowjobs <-.-> Tide --> |Retest and Merge| GitHub Horologium ---> |Create| Prowjobs PluginCat --> |Comment| GitHub PluginTrigger --> |Create| Prowjobs Sinker ---> |Garbage collect| Prowjobs Sinker --> |Garbage collect| Pods PCM -.-> |List and update| Prowjobs PCM ---> |Report| Prowjobs PCM ==> |Create and Query| Pods Prowjobs <-.-> |Inform| Crier --> |Report| GitHub

Notes

Note that Prow can also work with Gerrit, albeit with less features. Specifically, neither Tide nor Hook work with Gerrit yet.