How to pull image from Docker registry within Kubernetes cluster? - docker

Question

I'm learning Kubernetes and want to set up a Docker registry to run within my cluster, deploy any custom code to this private registry, then have my nodes pull images from this private registry to create pods. I've described my setup in this StackOverflow question
Originally I was caught up trying to figure out SSL certificates, but for now I've postponed that and I'm trying to work with an insecure registry. To that end I've created the following pod to run my registry (I know it's a pod and not a replica set or deployment -- this is only for experimental purposes and I'll make it cleaner once it's working):
apiVersion: v1
kind: Pod
metadata:
name: docker-registry
labels:
app: docker-registry
spec:
containers:
- name: docker-registry
image: registry:2
ports:
- containerPort: 80
hostPort: 80
env:
- name: REGISTRY_HTTP_ADDR
value: 0.0.0.0:80
I then created the following NodePort service:
apiVersion: v1
kind: Service
metadata:
name: docker-registry-external
labels:
app: docker-registry
spec:
type: NodePort
ports:
- targetPort: 80
port: 80
nodePort: 32000
selector:
app: docker-registry
I have a load balancer set up in front of my Kubernetes cluster which I configured to route traffic on port 80 to port 32000. So I can hit this registry at http://example.com
I then updated my local /etc/docker/daemon.json as follows:
{
"insecure-registries": ["example.com"]
}
With this I was able to push an image to my registry successfully:
> docker pull ubuntu
> docker tag ubuntu example.com/my-ubuntu
> docker push exapmle.com/my-ubuntu
The push refers to repository [example.com/my-ubuntu]
cc9d18e90faa: Pushed
0c2689e3f920: Pushed
47dde53750b4: Pushed
latest: digest: sha256:1d7b639619bdca2d008eca2d5293e3c43ff84cbee597ff76de3b7a7de3e84956 size: 943
Now I want to try and pull this image when creating a pod. So I created the following ClusterIP service to make my registry accessible within my cluster:
apiVersion: v1
kind: Service
metadata:
name: docker-registry-internal
labels:
app: docker-registry
spec:
type: ClusterIP
ports:
- targetPort: 80
port: 80
selector:
app: docker-registry
Then I created a secret:
apiVersion: v1
kind: Secret
metadata:
name: local-docker
type: kubernetes.io/dockerconfigjson
data:
.dockerconfigjson: ewoJImluc2VjdXJlLXJlZ2lzdHJpZXMiOiBbImRvY2tlci1yZWdpc3RyeS1pbnRlcm5hbCJdCn0K
The base64 bit decodes to:
{
"insecure-registries": ["docker-registry-internal"]
}
Finally, I created the following pod:
apiVersion: v1
kind: Pod
metadata:
name: test-docker
labels:
name: test
spec:
imagePullSecrets:
- name: local-docker
containers:
- name: test
image: docker-registry-internal/my-ubuntu
When I tried to create this pod (kubectl create -f test-pod.yml) and looked at my cluster, this is what I saw:
> kubectl get pods
NAME READY STATUS RESTARTS AGE
test-docker 0/1 ErrImagePull 0 4s
docker-registry 1/1 Running 0 34m
> kubectl describe pod test-docker
...
...
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled 3m33s default-scheduler Successfully assigned default/test-docker to pool-uqa-dev-3sli8
Normal Pulling 3m22s (x2 over 3m32s) kubelet Pulling image "docker-registry-internal/my-ubuntu"
Warning Failed 3m22s (x2 over 3m32s) kubelet Failed to pull image "docker-registry-internal/my-ubuntu": rpc error: code = Unknown desc = Error response from daemon: pull access denied for docker-registry-internal/my-ubuntu, repository does not exist or may require 'docker login'
Warning Failed 3m22s (x2 over 3m32s) kubelet Error: ErrImagePull
Normal SandboxChanged 3m19s (x7 over 3m32s) kubelet Pod sandbox changed, it will be killed and re-created.
Normal BackOff 3m18s (x6 over 3m30s) kubelet Back-off pulling image "docker-registry-internal/my-ubuntu"
Warning Failed 3m18s (x6 over 3m30s) kubelet Error: ImagePullBackOff
It's clearly failing to find the host "docker-registry-internal", despite the ClusterIP service.
I tried inspecting a pod from the inside using a trick I found online:
> kubectl run -i --tty --rm debug --image=ubuntu --restart=Never -- bash
If you don't see a command prompt, try pressing enter.
root#debug:/# cat /etc/hosts
# Kubernetes-managed hosts file.
127.0.0.1 localhost
::1 localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
fe00::0 ip6-mcastprefix
fe00::1 ip6-allnodes
fe00::2 ip6-allrouters
10.244.1.67 debug
It doesn't seem like ClusterIP services are being added to the /etc/hosts file, so I'm not sure how services are supposed to find one another?
I tried watching several Kubernetes tutorials on general service communication (e.g. an app pod communicating with a redis pod) and every time all they did was supply the service name as a host and it magically connected. I'm not sure if I'm missing something. Bear in mind I'm brand new to Kubernetes so the internals are still mystical to me.