add blog on how to use starlark in Woodpecker CI

Signed-off-by: prashant-gurung899 <prasantgrg777@gmail.com>

Author: prashant-gurung899

src/assets/woodpeckerCI/images/add.png

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+---
+title: Starlark in woodpecker CI
+authorName: Prashant Gurung
+authorAvatar: https://avatars.githubusercontent.com/u/53248463?v=4
+authorLink: https://github.com/prashant-gurung899
+createdAt: July 3, 2025
+tags: CI/CD
+banner: https://raw.githubusercontent.com/JankariTech/blog/woodpecker-ci-starlark/src/assets/woodpeckerCI/images/woodpecker.png
+---
+
+## Background
+Continuous Integration (CI) tools are vital for automating the testing and deployment of modern software. One such open-source tool is Woodpecker CI, a lightweight CI/CD system. Woodpecker CI is an open-source continuous integration and delivery platform that helps developers automate building, testing, and deploying their code. It is a community-driven fork and successor of the popular Drone CI project, sharing many design principles and compatibility with Drone pipelines. Traditionally, Woodpecker pipelines are written in YAML. But with the rise of programmable pipelines, we now have the flexibility to define our CI configuration using Starlark — a Python-like configuration language.
+
+In this blog, I’ll walk you through setting up Woodpecker CI with Traefik as a reverse proxy and integrating it with WCCS (Woodpecker Config Service) to convert Starlark configurations into YAML files, enabling us to write pipelines in .woodpecker.star files. Here's a high-level view of what we'll cover:
+
+- Spinning up a Woodpecker server
+
+- Authenticating with GitHub
+
+- Enabling a repository
+
+- Connecting WCCS with the Woodpecker server
+
+By the end, you’ll be able to write CI pipelines in Starlark and dynamically convert them to YAML during runtime.
+
+## Prepare Woodpecker secrets via .env
+```console
+Your woodpecker host
+WOODPECKER_HOST=https://<your-ci-server>
+
+
+# GitHub OAuth Secrets
+WOODPECKER_GITHUB_CLIENT=XXXXXXXXXXXXXXXX
+WOODPECKER_GITHUB_SECRET=XXXXXXXXXXXXXXXXXXXXXXXX
+
+
+# Shared secret used by server<->agent - you can generate it using openSSL
+WOODPECKER_AGENT_SECRET=<generated-secret>
+
+
+# Let’s Encrypt contact email (Traefik will use this)
+ACME_EMAIL=admin@example.com
+```
+
+## Traefik Configuration
+Traefik plays a crucial role in this architecture by handling all the networking complexities - SSL termination, routing, and load balancing
+
+```yml
+version: "3.9"
+
+services:
+  traefik:
+    image: traefik:v3.1
+    container_name: traefik
+    command:
+      - "--log.level=DEBUG"
+      - "--api.insecure=true"
+      - "--providers.docker=true"
+      - "--providers.docker.exposedbydefault=false"
+      - "--entrypoints.web.address=:80"
+      - "--entrypoints.websecure.address=:443"
+      - "--certificatesresolvers.letsencrypt.acme.httpchallenge=true"
+      - "--certificatesresolvers.letsencrypt.acme.httpchallenge.entrypoint=web"
+      - "--certificatesresolvers.letsencrypt.acme.email=${ACME_EMAIL}"
+      - "--certificatesresolvers.letsencrypt.acme.storage=/letsencrypt/acme.json"
+    ports:
+      - "80:80"
+      - "443:443"
+    volumes:
+      - "./letsencrypt:/letsencrypt"
+      - "/var/run/docker.sock:/var/run/docker.sock:ro"
+    networks:
+      - woodpecker-net
+```
+
+This configuration:
+
+- Sets up Traefik to listen on ports 80 and 443
+- Configures Let's Encrypt for automatic SSL certificate management
+- Enables Docker provider to automatically detect new services
+- Mounts necessary volumes for certificate storage and Docker socket access
+
+## Setting Up Woodpecker Server and Agent
+Now that we have Traefik running, let's set up the Woodpecker server and agent services. Here's the essential setup:
+
+```yml
+  woodpecker-server:
+    depends_on:
+      - wccs
+    image: woodpeckerci/woodpecker-server:v3
+    environment:
+      - WOODPECKER_LOG_LEVEL=debug
+      - WOODPECKER_OPEN=false
+      - WOODPECKER_HOST=${WOODPECKER_HOST}
+      - WOODPECKER_GITHUB=true
+      - WOODPECKER_GITHUB_CLIENT=${WOODPECKER_GITHUB_CLIENT}
+      - WOODPECKER_GITHUB_SECRET=${WOODPECKER_GITHUB_SECRET}
+      - WOODPECKER_AGENT_SECRET=${WOODPECKER_AGENT_SECRET}
+      - WOODPECKER_ADMIN=prashant-gurung899
+      - WOODPECKER_CONFIG_SERVICE_ENDPOINT=http://wccs:8080/ciconfig
+    volumes:
+      - woodpecker-server-data:/var/lib/woodpecker/
+    labels:
+      - "traefik.enable=true"
+      - "traefik.http.routers.woodpecker-secure.rule=Host(`your-ci-server`)"
+      - "traefik.http.routers.woodpecker-secure.entrypoints=websecure"
+      - "traefik.http.routers.woodpecker-secure.tls.certresolver=letsencrypt"
+      - "traefik.http.routers.woodpecker-secure.tls=true"
+      - "traefik.http.services.woodpecker-secure.loadbalancer.server.port=8000"
+      # HTTP router + redirect to HTTPS
+      - "traefik.http.routers.woodpecker-http.rule=Host(`your-ci-server`)"
+      - "traefik.http.routers.woodpecker-http.entrypoints=web"
+      - "traefik.http.routers.woodpecker-http.middlewares=redirect-to-https"
+      # Redirect middleware
+      - "traefik.http.middlewares.redirect-to-https.redirectscheme.scheme=https"
+    networks:
+      - woodpecker-net
+
+  woodpecker-agent:
+    image: woodpeckerci/woodpecker-agent:v3
+    command: agent
+    restart: always
+    depends_on:
+      - woodpecker-server
+    volumes:
+      - woodpecker-agent-config:/etc/woodpecker
+      - /var/run/docker.sock:/var/run/docker.sock
+    environment:
+      - WOODPECKER_LOG_LEVEL=debug
+      - WOODPECKER_SERVER=woodpecker-server:9000
+      - WOODPECKER_AGENT_SECRET=${WOODPECKER_AGENT_SECRET}
+    networks:
+      - woodpecker-net
+```
+
+## Authenticating with GitHub
+
+To connect GitHub with Woodpecker:
+
+1. Register a new OAuth application in your GitHub developer settings.
+
+2. Set the callback URL to `https://<your-ci-server>/authorize`
+
+3. Copy the generated Client ID and Secret.
+
+4. Use these values in the `WOODPECKER_GITHUB_CLIENT` and `WOODPECKER_GITHUB_SECRET` env vars.
+
+After that, you can log into the Woodpecker web UI using your GitHub account.
+
+## Enabling a Repository
+From the Woodpecker UI:
+
+- Select your GitHub repo.
+![Add Repo](https://raw.githubusercontent.com/JankariTech/blog/woodpecker-ci-starlark/src/assets/woopeckerCI/images/add.png)
+
+- Enable it for CI.
+![Enable Repo](https://raw.githubusercontent.com/JankariTech/blog/woodpecker-ci-starlark/src/assets/woopeckerCI/images/enable.png)
+
+Woodpecker will automatically add the necessary webhooks to the repo.
+
+
+## Generating the Public Key
+Every request sent by Woodpecker is signed using a http-signature by a private key (ed25519) generated on the first start of the Woodpecker server. You can get the public key for the verification of the http-signature from:
+```console
+http(s)://your-ci-server/api/signature/public-key
+```
+Store that public key into `keys/public.pem` in the same directory level as your docker compose, it will be needed for signature verification.
+
+## Setting Up WCCS-Woodpecker CI Config Service (Starlark Conversion Service)
+The Woodpecker Config Conversion Service (WCCS) is a lightweight web service created and maintained by [Opencloud-eu](https://opencloud.eu/en). It enables Woodpecker CI to convert pipeline definitions written in Starlark into standard YAML on the fly by receiving a signed POST request from Woodpecker.
+You can easily deploy WCCS using their official Docker image available on Docker Hub: [opencloudeu/wccs](https://hub.docker.com/r/opencloudeu/wccs).
+```yml
+  wccs:
+    image: opencloudeu/wccs:latest
+    container_name: wccs
+    command: server
+    environment:
+      - WCCS_LOG_LEVEL=debug
+      - WCCS_SERVER_PUBLIC_KEY=/keys/public.pem
+    volumes:
+      - /opt/woodpecker/keys:/keys
+      - /etc/ssl/certs:/etc/ssl/certs:ro
+    labels:
+      - "traefik.enable=true"
+      - "traefik.http.routers.wccs.rule=Host(`your-wccs-server`)"
+      - "traefik.http.routers.wccs.entrypoints=websecure"
+      - "traefik.http.routers.wccs.tls.certresolver=letsencrypt"
+      - "traefik.http.services.wccs.loadbalancer.server.port=8080"
+    networks:
+      - woodpecker-net
+
+volumes:
+  woodpecker-server-data:
+  woodpecker-agent-config:
+
+networks:
+  woodpecker-net:
+    driver: bridge
+```
+
+## Connecting WCCS with Woodpecker
+To allow Woodpecker to fetch pipeline configs from WCCS, we added this to the server env:
+```console
+WOODPECKER_CONFIG_SERVICE_ENDPOINT=http://wccs:8080/ciconfig
+```
+Woodpecker now sends a signed JSON payload to WCCS whenever a build is triggered. WCCS verifies the signature using the public key and responds with a YAML pipeline based on your .woodpecker.star file.
+
+## Sample Starlark Pipeline
+Here's a simple .woodpecker.star example:
+```console
+def main(ctx):
+    return [{
+        "name": "hello",
+        "steps": [
+            {
+                "name": "greeting",
+                "image": "alpine",
+                "commands": [
+                    "echo Hello from CI",
+                ],
+                "when": {
+                    "event": ["push", "pull_request"],
+                    "branch": ["master"],
+                },
+            }
+        ]
+    }]
+```
+This gets converted by WCCS into a valid Woodpecker pipeline YAML.
+
+## Conclusion
+This setup provides a robust, secure, and flexible CI/CD pipeline using Woodpecker CI, enhanced with WCCS for configuration management and protected by Traefik. The integration of these components creates a powerful system that can handle complex pipeline configurations while maintaining security and ease of use.
+
+Now, we can write pipelines in Starlark and let WCCS handle the conversion on the fly. This approach brings flexibility, structure, and the power of logic-based configurations to our CI pipelines.