Ensuring Correct IP Registration in Eureka

📌 Issue: Eureka Registers the Wrong IP (`169.254.x.x`)

🔍 Problem Statement

Auth-Service (running on Mac) was registered with 169.254.x.x (a link-local address) instead of its correct local network IP (192.168.x.x).
This caused gateway routing failures, as the wrong IP was unreachable.
As a result, remote debugging could not be triggered, making development and debugging impossible.
Even after fixing the registration, Eureka UI still showed stale 169.254.x.x instances.

🔹 Why Did This Happen?

1️⃣ How Eureka Determines an IP

When a service registers with Eureka, it tries to detect its IP in this order:

Checks if ip-address is set explicitly (eureka.instance.ip-address).
Checks if prefer-ip-address: true is enabled (forces Eureka to use an IP instead of hostname).
If no explicit IP is set, Eureka auto-selects the first available non-loopback interface.
If everything fails, Eureka resolves the hostname to an IP.

2️⃣ Why Was `169.254.x.x` Chosen Instead of `192.168.x.x`?

Multiple network interfaces on Mac (e.g., en0, lo0, bridge0).
Docker networking interference (Docker creates virtual networks that may confuse Eureka).
Eureka auto-detected the wrong interface (bridge0 or docker0).

✅ Fix: Ensure Eureka Registers the Correct IP

1️⃣ Explicitly Set the Correct IP in `application.yml`

Modify Auth-Service configuration:

eureka:
  instance:
    prefer-ip-address: true  # Forces Eureka to use an IP instead of hostname
    ip-address: ${HOST_IP}   # Uses dynamically assigned IP
    hostname: ${HOST_IP}     # Ensures consistency

Start the service with the correct IP:

HOST_IP=$(ipconfig getifaddr en0) java -jar auth-service.jar

(Replace en0 with the correct network interface if necessary.)

2️⃣ Reduce Eureka Stale Instance Timeout

Modify Eureka Server’s application.yml to clean up stale instances faster:

eureka:
  server:
    eviction-interval-timer-in-ms: 10000  # Eviction check every 10s
  client:
    registry-fetch-interval-seconds: 5  # Refresh UI every 5s

3️⃣ Manually Remove Stale Instance

Find the incorrect instance ID:

curl -s http://192.168.1.105:8761/eureka/apps/AUTH-SERVICE | grep instanceId

Delete the old entry:

curl -X DELETE http://192.168.1.105:8761/eureka/apps/AUTH-SERVICE/{INSTANCE_ID}

(Replace {INSTANCE_ID} with the correct ID.)

4️⃣ Restart Eureka to Force Cleanup

If the wrong IP persists, restart Eureka:

docker restart eureka-server

Or (if running standalone):

pkill -f eureka && java -jar eureka-server.jar

5️⃣ Check Current Eureka Connection (More Reliable than Web UI)

To verify Eureka’s registered instance IP, use:

curl -s http://192.168.1.105:8761/eureka/apps/AUTH-SERVICE | grep ipAddr

✅ This command is more accurate than the Eureka web UI, as it directly fetches the latest registered instances.

🎯 Final Outcome

✔ Auth-Service is now registered only with 192.168.x.x.

✔ Eureka UI no longer shows 169.254.x.x.

✔ Gateway correctly routes requests to the correct IP, ensuring full functionality.

✔ Remote debugging now works correctly, allowing normal development and testing.

✔ Stale instances are evicted quickly and automatically.

✔ Checking via curl ensures accurate real-time Eureka registration info.

📌 Issue: Eureka Registers the Wrong IP (169.254.x.x)