Kubernetes is awesome. But it is very annoying to be halfway through a guide just to have that guide “drop into” docker. Kubernetes _can_ use docker, but it doesn’t _need_ docker. In particular, this is true of microk8s. If you have your kubernetes cluster because of microk8s, you won’t have docker installed.
As an alternative to “docker build”, you can use buildah – “a tool that builds Open Container Initiative (OCI) container images”. All that needs done is (1) translate those “docker xxx” commands to buildah, and (2) navigate the registries so that your buildah-built image ends up somewhere that your kubectl can use it.
Dockerfile – original
FROM openjdk:11-jre-slim
WORKDIR /app
COPY target/java-hello-world-0.0.1.jar java-hello-world.jar
ENTRYPOINT ["java", "-jar", "/app/java-hello-world.jar"]
EXPOSE 8080
(Gads – a little side note here: WordPress by default allows .doc file types, but denies .txt file types “for security reasons”. It brings into doubt WordPress’s concept of ‘security’. )
Note: there are two machines here: “bld$” is the prompt of the buildah machine. “k8s$” is the prompt of the microk8s kubernetes machine.
0. Diversion – create the target/java-hello-world-0.0.1.jar file by installing java, cloning source from github. You can skip this step if you already have a java .jar file.
Diversion: install java, create java-hello-world-0.0.1.jar
bld$ sudo apt install openjdk-11-jdk-headless
bld$ git clone https://github.com/bmuschko/ckad-study-guide.git
bld$ cd ckad-study-guide/ch02/containerized-java-app
bld$ ./mvnw package spring-boot:repackage
...snip...
bld$ ls -hl target/java-hello-world-0.0.1.jar
-rw-rw-r-- 17M Jun 8 23:53 target/java-hello-world-0.0.1.jar
1. Install buildah, fix the Dockerfile, and create the container image.
Command: install buildah and java
bld$ sudo apt-get -y install buildah
Dockerfile – fixed for buildah
FROM docker.io/openjdk:11-jre-slim
WORKDIR /app
COPY target/java-hello-world-0.0.1.jar java-hello-world.jar
ENTRYPOINT ["java", "-jar", "/app/java-hello-world.jar"]
EXPOSE 8080
Command: build with buildah
bld$ buildah bud -t java-hello-world:1.0.0 .
-- NOTE: "buildah images" is the correct command to list images
bld$ buildah images
REPOSITORY TAG IMAGE ID CREATED SIZE
localhost/java-hello-world 1.0.0 a24b49859451 7 weeks ago 241 MB
-- Note: "buildah list" == "buildah containers" == not the correct command
-- at this step in the process. kept here only for historical purposes.
bld$ buildah list
CONTAINER ID BUILDER IMAGE ID IMAGE NAME CONTAINER NAME
39d1427e4dad * a24b49859451 localhost/java-hello-world:1.0.0 java-hello-world-working-container
At this time, you have a OCI container image.
- (Diversion – create a registry using “buildah run”. Push the container image.)
Diversion: running a registry with buildah run
# NOTE: these steps are not required. The goal is to get it to your microk8s registry, not to create another registry as done here:
bld$ registry=$(buildah from registry)
bld$ buildah run $registry
bld$ buildah push --tls-verify=false java-hello-world:1.0.0 docker://localhost:5000/java-hello-world/java-hello-world:1.0.0
2. Start microk8s registry, collect IP information
Command: Start the microk8s registry
k8s$ microk8s enable registry
The registry will be created with the default size of 20Gi.
You can use the "size" argument while enabling the registry, eg microk8s.enable registry:size=30Gi
Addon storage is already enabled.
Applying registry manifest
namespace/container-registry created
persistentvolumeclaim/registry-claim created
deployment.apps/registry created
service/registry created
configmap/local-registry-hosting configured
The registry is enabled
$ kubectl get po -A | grep registry
container-registry registry-9b57d9df8-hp79v 1/1 Running 0 3d19h
k8s$ kubectl get po --namespace=container-registry registry-9b57d9df8-hp79v -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
registry-9b57d9df8-hp79v 1/1 Running 0 3d19h 10.1.119.169 ub2004microk8stwo
k8s$ echo 10.1.119.169 is not "externally available"
k8s$ kubectl get no -o wide | grep ub2004microk8stwo
ub2004microk8stwo Ready 211d v1.19.10-34+8f8eec7c3f1428 10.0.1.80 Ubuntu 20.04 LTS 5.4.0-72-generic containerd://1.3.7
k8s$ REGISTRY=10.0.1.80:32000
Command: Push from buildah machine to microk8s registry
bld$ REGISTRY=10.0.1.80:32000
bld$ buildah push --tls-verify=false java-hello-world:1.0.0 ${REGISTRY}/java-hello-world:1.0.0
Command: Confirm the image is in the registry
k8s$ REGISTRY=10.0.1.80:32000
k8s$ curl http://$REGISTRY/v2/_catalog
{"repositories":["java-hello-world"]}
k8s$ curl http://$REGISTRY/v2/java-hello-world/tags/list
{"name":"java-hello-world","tags":["1.0.0"]}
deployment.yaml – using minik8s registry as image source
apiVersion: apps/v1
kind: Deployment
metadata:
name: exported-java-deployment
labels:
app: exportedjava
spec:
selector:
matchLabels:
app: exportedjava
template:
metadata:
labels:
app: exportedjava
spec:
containers:
- name: java-hello-world
image: localhost:32000/java-hello-world:1.0.0
imagePullPolicy: Never
ports:
- containerPort: 8080
Command: Apply the deployment
k8s$ kubectl apply -f deployment.yaml
Command: Test deployment
k8s$ kubectl get po -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
exported-java-deployment-54cbc44997-ttgxc 1/1 Running 0 103s 10.1.119.149 ub2004microk8stwo
k8s$ curl http://10.1.119.149:8080
Hello World!
(Miscellaneous commands – query running containers for image names and sizes)
Command: Show running images – names and sizes
k8s$ kubectl get nodes -o json | jq '.items[].status.images[] | .names[1], .sizeBytes'
"docker.io/bitnami/mongodb:4.4.2-debian-10-r27"
180259295
"docker.io/kubernetesui/dashboard:v2.0.0"
66209190
"docker.io/coredns/coredns:1.6.6"
12932169
"k8s.gcr.io/pause:3.1"
317164
"localhost:32000/java-hello-world:1.0.0"
97008161
Command: Alternative way to copy/import image
-- FAILS, wrong way to "push"/export the image
bld$ buildah push 1bb7f7cb0d2c dir:/tmp/1bb7f7cb0d2c
Getting image source signatures
Copying blob 40093787e10f done
Copying blob e1929b65aa97 done
Copying blob 1b739069a094 done
Copying blob 2655e3fdba88 done
Copying blob d32026d4252e done
Copying blob c76dc6af9411 done
Copying blob 89efdf5cc8ae done
Copying blob d9b44548153b done
Copying blob 8f2b297d408f done
Copying blob 89f7fb50be94 done
Copying config 1bb7f7cb0d done
Writing manifest to image destination
Storing signatures
$bld tar cvf 1bb7f7cb0d2c.tar ./1bb7f7cb0d2c/
$bld scp 1bb7f7cb0d2c.tar k8s:~
k8s$ mkcrok8s ctr image import 1bb7f7cb0d2c.tar
ctr: unrecognized image format
-- Fail.
-- Correct way to 'buildah push", but incorrect way to create .tar file, FAILS:
bld$ buildah push 1bb7f7cb0d2c oci:/tmp/oci-path:localhost/mysimpleapi:1.0.0
bld$ cd /tmp
bld$ tar cvf oci-path.tar ./oci-path
k8s$ microk8s ctr image import oci-path.tar
ctr: unrecognized image format
-- Correct way to create the .tar file: WORKS:
bld$ cd /tmp
bld$ cd oci-path
bld$ tar cvf ../mysimpleapi.tar .
bld$ scp
k8s$ microk8s ctr image import mysimpleapi.tar
unpacking localhost/mysimpleapi:1.0.0 (sha256:xxxxxx)...done
k8s$ microk8s ctr image list -q | grep mysimpleapi
localhost/mysimpleapi:1.0.0
