GAE appliation to automatically clean up after dangling GCP load balancers

BEWARE! DELETES GCP RESOURCES! USE AT YOUR OWN PERIL!

For a longer discussion, please read my post

As of this writing (Dec 2017), the following steps almost always leave dangling HTTP(s) LBs (dangling meaning the backend instances/instance groups are long gone, but resources such as the forwarding rules and target proxies are still alive):

1. Create a GKE cluster
2. Create Ingress resources in said cluster (note: I create them through kube-lego)
3. Delete the GKE cluster (either via CLI or Web Console)

The dangling load balancers are there because when a GKE cluster is deleted, the VMs and the master nodes are just killed without allowing Kubernetes to gracefully clean up after itself (I'm not even sure if it's possible for GKE to perform a global destruction type of unloading).

This is my attempt to not having to worry about this anymore. I hope Google fix things so I no longer have to worry about somebody (myself included) randomly decides to delete a cluster used for development, only to find that dangling load balancers were adding up to your monthly bill.

The basic mode of operations is as follows:

1. Look for forwarding rules that starts with "k8s-fw"
2. Find the corresponding target http(s) proxies
3. Find the corresponding url maps
4. Find the corresponding backend services
5. Find the corresponding instance groups
6. Find the corresponing instances

If the instances list comes up empty, we declare this url map "dead". If all the url maps in the target proxy are dead, then we declared this target proxy "dead". If all the target proxies are dead, we declare this forwarding rule "dead".

We delete the corresponding forwarding rule, backend services, healthchecks, and SSL certificates along with it.

There's another possibility: We could have load balancers dangling while it failed to properly initialize and there are no corresponding forwarding rules. In order to catch these, we look for target http(s) proxies that have not yet been found during the search in the above operation, and check those as well.

Both of these combined will cover most cases.

Lastly, the target proxy for the corresponding load balancers must be at least 1 hour old in order to be deleted. This is to prevent accidental deletes while the proxies are being initialized.

Ingress creates firewall rules to allow healthchecks to go through to your nodes. And... these can be left dangling as well.

Each firewall rule contains a target tag, and if it matches a non-existent "gke-*" tag, thes will be deleted, too

(UNIMPLEMENTED)

Sometimes Service resources are also left dangling (probably when "LoadBalancer" mode is used).

1. Look for forwarding rules with description matching "kubernets.io/service-name"
2. Find the corresponding target pool
3. Find the corresponding instances

If there are no active instances in the target pool, then the target pool is delcared "dead", and so is the forwarding rule.

We delete the corresponding forwarding rule and target pool.

gcloud app deploy .

You should probably deploy the contents of cron.yaml, but note that if you just do gcloud app deploy cron.yaml, it will overwrite any existing cron configuration. If you have a main cron.yaml that you already use, merge the contents of this cron.yaml to that file and deploy from there.