get the k3d local registry working with tilt

[clux]

supposedly this is pretty easy. made a registry node for my k3d, but it still pushed to my dockerhub. might need to create the cluster with the either --registry-create or --registry-use.

anyway want the tilt up experience working for users, and currently it won't because it needs to push to my dockerhub.

• try to follow https://k3d.io/usage/guides/registries/#using-a-local-registry and make it work
• link to that guide in the readme (we already mention the local registry)
• keep it simple enough so that we don't have to pollute the readme in this repo with linux specifics
• some fallback mechanic if they don't have a k3d cluster?
• test with k3d 5

suggestions welcome, coming back to this at some point.

[clux]

doing a registry import for CI now correctly via #138

... although doing the same in the README might be too complex for a starter project. users would need to do a --registry create name and we need to k3d image import --cluster clustername from what got built, and it feels like a lot of juggling.

[clux]

managed to get this to work. not entirely sure what i did tbh.

i created a registry with a basic creator command:

 k3d cluster create 31 --servers 1 --registry-create r31 --no-rollback '--image=rancher/k3s:v1.31.5-k3s1' --k3s-arg '--disable=traefik,servicelb,metrics-server@server:*'

and hooked it up to the tiltfile with:

# Using a local k3d registry to locally docker push into. https://k3d.io/v5.2.0/usage/registries/#using-a-local-registry
# Substitute for the registry name passed via k3d cluster create --registry-create=NAME
REG='k31'
default_registry(REG + ':5000', host_from_cluster='localhost:5000')

which seemed to make it work, but then looking at the logs it was actually printing

Auto-detected local registry from environment: &RegistryHosting{Host:localhost:41681,HostFromClusterNetwork:r31:5000,HostFromContainerRuntime:r31:5000,Help:https://k3d.io/stable/usage/registries/#using-a-local-registry,SingleName:,}
Default registry specified, but will be ignored in favor of auto-detected registry.

and sure enough, it worked again without those. leaving it as a comment here incase i need it in the future. pushing a commit to close it because it works.

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sidenote: seems like there's a LOT of magic in tilt.

• image name injection: need to just ensure we set some image name and use it consistently, and tilt will just magically inject it into the yaml when i do k8s_yaml meaning what i name it before that is just for the benefit of tilt's string replace.
• registry detection overrides explicit default_registry
• context whitelist allow_k8s_contexts is ignored by local cluster detection, and also doesn't support globs to make it usable anyway