7-migration

Step 7: Migration

In this step, we will make the web service talk to the API service on Kubernetes. We will do so with zero-downtime and without making any changes to the running web service.

Goals

• Switch the web service talk to the api service on Kubernetes without downtime.

Tasks

Windows users: Instead of editing /etc/hosts, shut down the API service that was running on the VM. Traffic should get routed over to the API service running on Kubernetes. Skip to the "Verify" section.

Switch local DNS

At this point, we still have our api-vm service running locally. Confirm that web is still talking to the api-vm by going to http://localhost:8080.

To perform the switch with zero-downtime, we will mimic using DNS by changing the api's service IP in /etc/hosts, similarly to how we did it in step 1.

Currently, our /etc/hosts file points at 127.0.0.1, which is the IP the api-vm service binds to.

api-k8s service is exposed via Kubernetes ingress which is bound to 0.0.0.0. As long as we point api at an IP other than 127.0.0.1, but the one our machine understands, it should go to the ingress IP, i.e. 0.0.0.0. We will point api at ::1 (ipv6 IP for localhost).

Open the /etc/hosts file:

sudo vim /etc/hosts

Modify the line that points to api service and change it to ::1:

::1 api

Verify

First, go to http://localhost:8080/ui again and confirm that the web service is now talking to the api-k8s service instead.

Second, go to the Grafana UI and check the request rate of the API service by running rate(handle_request_http_seconds_count[5m]) query. (refresh the http://localhost:8080/ui page a few times to generate more metrics).

Conclusion

We have migrated our API service to Kubernetes with zero downtime!

Next Step

Go to 8-consul.