LinkLab — Week 5 Blueprint

CS4297 Applied System Design · CI/CD with Forgejo Actions + ElasticSearch

Complete Week 4 solution included. Clone this and start here.

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What you are building this week

Part	What happens	Time
A	Push to Forgejo, set up Actions pipeline, trigger first green build	30 min
B	Implement ElasticSearch indexing and search endpoint	50 min
C	Observe the fan-out pattern across all four datastores	15 min
Optional 1	Multi-field search with custom ES query and fuzziness	30 min
Optional 2	Pipeline notification — post PR comment after deploy	30 min
Optional 3	Re-index endpoint — rebuild ES index from MySQL	30 min

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Prerequisites

• IntelliJ IDEA Ultimate — free at jetbrains.com/student
• JDK 21 — check with java -version
• Docker Desktop with at least 6 GB RAM (Settings → Resources → Memory)
• Forgejo account — register at cs4297.skynet.ie

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Getting started

1. Start the infrastructure

docker compose up -d mysql redis dynamodb-local dynamodb-admin elasticsearch kibana

ElasticSearch takes ~30 seconds to become healthy. Kibana takes another ~30 seconds after that.

docker compose ps   # all should show "healthy" or "running"

2. Run the application

From IntelliJ: open LinkLabApplication.kt and click ▶

From terminal (Mac/Linux): ./gradlew bootRun From terminal (Windows): .\gradlew.bat bootRun

3. Run the tests

# Mac/Linux
./gradlew test

# Windows
.\gradlew.bat test

Before you've written any code, this will fail to compile — not just fail tests — with errors like Unresolved reference 'findByOriginalUrlContaining'. That's expected: LinkSearchServiceTest already calls the method you add in Part B step 1, and Kotlin compiles all test files together, so one missing method blocks the whole test task. Add the one-line method signature to LinkSearchRepository first (Part B step 1), then re-run — you should see:

• LinkServiceTest, LinkControllerTest, CacheTest, ClickEventServiceTest, GlobalExceptionHandlerTest — all pass (Week 4 complete)
• LinkSearchServiceTest — 5 tests fail until you implement the rest of Part B. Expected.
• SearchControllerTest — 4 tests fail until you implement SearchController.search() and reindex(). Expected.

4. Open Kibana

Visit http://localhost:5601

Go to Dev Tools (wrench icon, left sidebar) and run:

GET /_cluster/health

You should see "status": "green" or "yellow" (yellow is fine for single-node).

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What to implement

src/main/kotlin/ie/ul/cs4297/linklab/
├── search/
│   ├── LinkDocument.kt              # Already complete — read it
│   ├── LinkSearchRepository.kt      # PART B: add findByOriginalUrlContaining()
│   └── LinkSearchService.kt         # PART B: implement index() and search()
└── controller/
    └── SearchController.kt          # PART B: implement GET /api/links/search?q=

src/main/kotlin/ie/ul/cs4297/linklab/service/
└── LinkService.kt                   # PART B: uncomment linkSearchService.index() call

Implement in this order:

1. LinkSearchRepository — add the derived query method
2. LinkSearchService.index() — save to ES, never throw
3. LinkSearchService.search() — query ES, return empty list if unavailable
4. SearchController.search() — validate input, return results
5. LinkService.shorten() — uncomment the ES index call

Everything else is the complete Week 4 solution. Do not modify it.

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Setting up the Forgejo Actions pipeline (Part A)

1. Create your Forgejo repository

Log in to cs4297.skynet.ie and create a new repo named cs4297-linklab.

2. Push this blueprint to Forgejo

git remote set-url origin https://cs4297.skynet.ie/<your-username>/cs4297-linklab.git
git push -u origin main

3. Add a secret for the container registry

• Forgejo → avatar → Settings → Applications → generate token (ci-token, scope: write:package)
• Repository → Settings → Secrets → Actions → New secret
• Name: ACCESS_TOKEN, value: your token

4. Trigger the pipeline

Create a branch, commit, push, open a PR on Forgejo, merge it. Watch the pipeline run under repository → Actions tab.

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Fan-out pattern — four datastores

After implementing Part B, POST /api/links writes to:

Store	Purpose	Fails gracefully?
MySQL	Source of truth	No
Redis cache	Fast redirects	Yes
Redis leaderboard	Click ranking	Yes
ElasticSearch	Full-text search	Yes

Week 6 (Kafka) makes the ES and leaderboard writes asynchronous.

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Week-by-week progression

Week	Content	Blueprint
2	REST API + MySQL	Stubs for LINK-001
3	Docker · Redis · NGINX · Grafana	Complete Week 2
4	SQL vs NoSQL · DynamoDB	Complete Week 3
5	CI/CD · ElasticSearch · Fan-out	← you are here
6	Kafka async pipeline	Complete Week 5
7	JWT + OAuth2	Complete Week 6
8	Kubernetes	Complete Week 7
9	Capstone: full integration	Complete Week 8

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Common issues

ElasticSearch crashes on startup Docker Desktop doesn't have enough memory. Increase to at least 6 GB in Settings → Resources → Memory.

ConnectException to ElasticSearch on bootRun ES is not yet healthy. Run docker compose ps and wait until ES shows healthy.

LinkSearchServiceTest fails with UnsatisfiedDependencyException The ES auto-config is not excluded in the test profile. Check application-test.properties has the five spring.autoconfigure.exclude entries.

Pipeline fails at the Docker push step ACCESS_TOKEN secret is missing or has wrong scope. It needs write:package.

Kibana shows "Kibana server is not ready yet" Wait another 30 seconds — Kibana waits for ES to be fully ready before starting.

./gradlew bootRun fails with java.lang.IllegalArgumentException Gradle is using JDK 25. Run .\gradlew --stop then set Gradle JVM to Java 21 in IntelliJ Settings → Build Tools → Gradle → Gradle JVM.