Docker Trusted Registry (DTR) in a Docker Enterprise Edition (EE) cluster allows users to create a private image repository for their own use. They may want to do this when they want to use the cluster for their work but don’t want to or can’t use their own system or they’re not ready yet to share it with others. However, using a private image repository in a Kubernetes deployment requires some additional steps. In this post, I will show you how to setup the repository and use it in your deployment.

In the example below, we’re going to create an image repository in DTR for an nginx image for the user ken.rider.

In this case, we’re going to use the official image for nginx as the basis for the nginx image in our repository. We’ll need to pull the image from the Docker Hub, login to DTR on our cluster, re-tag the image for our repository and push the image to DTR.

ken> docker image pull nginx:1.14-alpine
1.14-alpine: Pulling from library/nginx
6c40cc604d8e: Already exists
76679ad9f124: Pull complete
389a52582f93: Pull complete
496e2dd2b91a: Pull complete
Digest: sha256:b96aeeb1687703c49096f4969358d44f8520b671da94848309a3ba5be5b4c632
Status: Downloaded newer image for nginx:1.14-alpine
ken> docker login ken-dtr.lab.capstonec.net
Username: ken.rider
Password:
Login Succeeded
ken> docker image tag nginx:1.14-alpine ken-dtr.lab.capstonec.net/ken.rider/nginx:1.14-alpine
ken> docker image push ken-dtr.lab.capstonec.net/ken.rider/nginx:1.14-alpine
The push refers to repository [ken-dtr.lab.capstonec.net/ken.rider/nginx]
129ba078f157: Layer already exists
8c8f1eccd524: Layer already exists
68442845474f: Layer already exists
503e53e365f3: Layer already exists
1.14-alpine: digest: sha256:b9734546761e49b453efce35ee523bbcaff1052d281516f133d41b090e26c0df size: 1153

As an alternative, an administrator can change the DTR setting to create a repository on push. In this case, the repository is set to private by default.

Here the user only has to push the image to create the private image repository.

ken> docker image pull alpine
Using default tag: latest
latest: Pulling from library/alpine
6c40cc604d8e: Already exists
Digest: sha256:b3dbf31b77fd99d9c08f780ce6f5282aba076d70a513a8be859d8d3a4d0c92b8
Status: Downloaded newer image for alpine:latest
ken> docker login ken-dtr.lab.capstonec.net
Username: ken.rider
Password:
Login Succeeded
ken> docker image tag alpine ken-dtr.lab.capstonec.net/ken.rider/alpine:latest
ken> docker image push ken-dtr.lab.capstonec.net/ken.rider/alpine:latest
The push refers to repository [ken-dtr.lab.capstonec.net/ken.rider/alpine]
503e53e365f3: Mounted from ken.rider/nginx
latest: digest: sha256:25b4d910f4b76a63a3b45d0f69a57c34157500faf6087236581eca221c62d214 size: 528

Here’s what we see in DTR after we push both images. Note that each repository is labeled as private.

Now, let’s create a Kubernetes service based on the nginx image from this private repository in DTR. (If you would like to know more about the user-kenrider namespace used below, see my previous post on how to Create a User K8S Sandbox in Docker EE.)

ken> kubectl --namespace user-kenrider create deployment nginx --image=ken-dtr.lab.capstonec.net/ken.rider/nginx:1.14-alpine
deployment.extensions "nginx" created

That looks promising. Let’s look at the deployment.

ken> kubectl --namespace user-kenrider get deployments
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
nginx 1 1 1 0 25s
ken> kubectl --namespace user-kenrider describe deployment nginx
Name: nginx
Namespace: user-kenrider
CreationTimestamp: Sun, 03 Feb 2019 15:26:41 -0700
Labels: app=nginx
Annotations: deployment.kubernetes.io/revision=1
Selector: app=nginx
Replicas: 1 desired | 1 updated | 1 total | 0 available | 1 unavailable
StrategyType: RollingUpdate
MinReadySeconds: 0
RollingUpdateStrategy: 1 max unavailable, 1 max surge
Pod Template:
Labels: app=nginx
Containers:
nginx:
Image: ken-dtr.lab.capstonec.net/ken.rider/nginx:1.14-alpine
Port:
Host Port:
Environment:
Mounts:
Volumes:
Conditions:
Type Status Reason
---- ------ ------
Available True MinimumReplicasAvailable
Progressing True ReplicaSetUpdated
OldReplicaSets:
NewReplicaSet: nginx-659f44b5b4 (1/1 replicas created)
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal ScalingReplicaSet 42s deployment-controller Scaled up replica set nginx-659f44b5b4 to 1

Notice that the deployment says it has scaled up to 1 replica but the 1 replica is unavailable.

Let’s look at the pods.

ken> kubectl --namespace user-kenrider get pods
NAME READY STATUS RESTARTS AGE
nginx-659f44b5b4-f7bz2 0/1 ImagePullBackOff 0 1m
ken> kubectl --namespace user-kenrider describe pod nginx-659f44b5b4-f7bz2
Name: nginx-659f44b5b4-f7bz2
Namespace: user-kenrider
Priority: 0
PriorityClassName:
Node: ip-172-31-14-17/172.31.14.17
Start Time: Sun, 03 Feb 2019 15:26:42 -0700
Labels: app=nginx
pod-template-hash=2159006160
Annotations:
Status: Pending
IP: 192.168.87.199
Controlled By: ReplicaSet/nginx-659f44b5b4
Containers:
nginx:
Container ID:
Image: ken-dtr.lab.capstonec.net/ken.rider/nginx:1.14-alpine
Image ID:
Port:
Host Port:
State: Waiting
Reason: ImagePullBackOff
Ready: False
Restart Count: 0
Environment:
Mounts:
/var/run/secrets/kubernetes.io/serviceaccount from default-token-kjtft (ro)
Conditions:
Type Status
Initialized True
Ready False
ContainersReady False
PodScheduled True
Volumes:
default-token-kjtft:
Type: Secret (a volume populated by a Secret)
SecretName: default-token-kjtft
Optional: false
QoS Class: BestEffort
Node-Selectors:
Tolerations: com.docker.ucp.manager
node.kubernetes.io/not-ready:NoExecute for 300s
node.kubernetes.io/unreachable:NoExecute for 300s
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled 1m default-scheduler Successfully assigned user-kenrider/nginx-659f44b5b4-f7bz2 to ip-172-31-14-17
Normal Pulling 40s (x3 over 1m) kubelet, ip-172-31-14-17 pulling image "ken-dtr.lab.capstonec.net/ken.rider/nginx:1.14-alpine"
Warning Failed 40s (x3 over 1m) kubelet, ip-172-31-14-17 Failed to pull image "ken-dtr.lab.capstonec.net/ken.rider/nginx:1.14-alpine": rpc error: code = Unknown desc = Error response from daemon: pull access denied for ken-dtr.lab.capstonec.net/ken.rider/nginx, repository does not exist or may require 'docker login'
Warning Failed 40s (x3 over 1m) kubelet, ip-172-31-14-17 Error: ErrImagePull
Normal BackOff 2s (x5 over 1m) kubelet, ip-172-31-14-17 Back-off pulling image "ken-dtr.lab.capstonec.net/ken.rider/nginx:1.14-alpine"
Warning Failed 2s (x5 over 1m) kubelet, ip-172-31-14-17 Error: ImagePullBackOff

Here we see the pod tried to pull the ken-dtr.lab.capstonec.net/ken.rider/nginx:1.14-alpine image but failed. Notice it says we may need to login to DTR. How do we do that securely with a deployment/pod? We start by going to Pull an Image from a Private Registry in the Kubernetes reference documentation. There we see we need to create a Kubernetes secret with the user login information and pass that information in the pod specification.

Let’s start by creating the secret.

ken> kubectl --namespace user-kenrider create secret docker-registry regcred --docker-server=https://ken-dtr.lab.capstonec.net --docker-username=ken.rider --docker-password=mypassword --docker-email=ken.rider@capstonec.com
secret "regcred" created

Then we’ll create a Kubernetes manifest, named deployment-nginx.yml, using this secret in the pod specification.

kind: Deployment
apiVersion: extensions/v1beta1
metadata:
  labels:
    app: nginx
  name: nginx
  namespace: user-kenrider
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - image: ken-dtr.lab.capstonec.net/ken.rider/nginx:1.14-alpine
        imagePullPolicy: IfNotPresent
      name: nginx
      imagePullSecrets:
      - name: regcred

Now we’ll delete the previous deployment and apply this manifest file that specifies the secret we created. (We could have just done an apply but wanted to be explicit for this post.) And this time we can see the deployment is available and the pod is running.

ken> kubectl --namespace user-kenrider delete deployment nginx
deployment.extensions "nginx" deleted
ken> kubectl --namespace user-kenrider apply -f .\deployment-nginx.yml
deployment.extensions "nginx" created
ken> kubectl --namespace user-kenrider get deployments
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE

nginx 1 1 1 1 15s
ken> kubectl --namespace user-kenrider get pods
NAME READY STATUS RESTARTS AGE

nginx-67476dd867-5gw44 1/1 Running 0 24s

In this post we’ve seen how to create a private image repository in DTR on a Docker EE cluster and how to use an image from that private repository in a Kubernetes deployment on that same cluster.