bug: The upstream associated with other routes cannot be deleted, and the delete event keeps retrying

[Donghui0]

Issue description

controller log as below:

upstream delete failed, The delete event is added to the queue again.

Environment

• apisix-ingress-controller version: v0.5.0
• Kubernetes cluster version: v1.16.9

Minimal test code / Steps to reproduce the issue

1. create apisix route, service field references an existing k8s service.
2. delete apisix route resouce

What's the actual result? (including assertion message & call stack if applicable)

the delete event keeps retrying....

What's the expected result?

ignore related upstream

add resp.StatusCode != 400 condition ?

[tokers]

We may need to handle the given error from the caching operation.

[tokers]

We may need to handle the given error from the caching operation.

Ignore this please.

[tokers]

@Donghui0 Thanks for your report, I have captured the root reason about this bug, I will fix it.