Remove tianon/true as the "nop" image

[ghost]

Expected Behavior

The "nop" image that Pipelines uses to stop Sidecars should be available.

Edit: Generally, my hunch here is that we shouldn't be depending on external images for core Pipelines functionality at all but I'm open to dialog on that if it's simply not possible.

Actual Behavior

It appears that the SHA for tianon/true, our current "nop" image, has changed in Docker Hub and results in errors like this in TaskRun Pod logs:

  Normal   Pulling    2s    kubelet, gke-sidecars-default-pool-2579a152-cb5d  Pulling image "tianon/true@sha256:183cb5fd54142948ad88cc986a217465cfe8786cfdd89b1ed1fc49825da413a7"
  Warning  Failed     2s    kubelet, gke-sidecars-default-pool-2579a152-cb5d  Failed to pull image "tianon/true@sha256:183cb5fd54142948ad88cc986a217465cfe8786cfdd89b1ed1fc49825da413a7": rpc error: code = Unknown desc = Error response from daemon: received unexpected HTTP status: 500 Internal Server Error
  Warning  Failed     2s    kubelet, gke-sidecars-default-pool-2579a152-cb5d  Error: ErrImagePull

Steps to Reproduce the Problem

1. Create a fresh cluster to make sure that the tianon/true image isn't cached on a Node
2. Deploy Tekton Pipelines
3. kubectl create -f ./examples/v1beta1/taskruns/sidecar-interp.yaml

Notice that the Pod underlying the TaskRun will fail with a ErrImagePull

Additional Info

• Kubernetes version:

1.16.8

• Tekton Pipeline version:

master branch, but also affects 0.12 and 0.11 releases.

[vincent-pli]

Fixed by #2713 should be closed

[vdemeester]

I guess so too but, @sbwsg if not using tianon/true, which image would we use ? 🤔

[ghost]

we could either bring back our pipeline-owned nop image, or go with a different strategy. i have been wondering what would happen on various platforms if we just replaced the image with a non-existent one, for example.