Scaling

Now that you have the application data moved to an external service, we can safely scale our application up to more than one instance. After all, running a single instance of something is a recipe for an outage.

• Scale your app to two instances:

  cf scale first-push -i 2
  

  You should see output like:

  Scaling app first-push in org cloudfoundry-training / space development as steve@example.com...
  OK
  

Checking your work

You can see the status of your app by running cf app first-push:

Showing health and status for app first-push in org cff / space work as steve@example.com...

name:              first-push
requested state:   started
routes:            first-push-responsible-roan.<some-domain>
last uploaded:     Sun 31 Mar 11:47:05 MDT 2020
stack:             cflinuxfs3
buildpacks:        go

type:           web
instances:      2/2
memory usage:   64M
     state     since                  cpu    memory         disk          details
#0   running   2020-03-31T18:30:42Z   0.2%   10.2M of 64M   14.6M of 1G   
#1   running   2020-03-31T18:34:46Z   0.3%   9.5M of 64M    14.6M of 1G 

If you refresh your app in a browser multiple times, you will see the App Instance Index change (once the new instance has fully started and is available). Cloud Foundry is load balancing your requests across both instances.

What happened?

Remember that image Cloud Foundry created when you pushed the app? Cloud Foundry grabbed a cached version of it and started a new container. When the app became available, Cloud Foundry started routing traffic to it. With multiple instances running, Cloud Foundry load balances traffic across them.

And what didn’t happen?

Just like on a push, no creating resources. No updating routing tables. No updating load balancers. Just cf scale.

Now that we have two instances running, let’s crash one and see what happens.