Single node cluster orchestration for go application with minimum effort
Installion instruction for kubectl and minikube
Start minikube:
minikube start
To install and run Kubernetes on Mac follow this
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: go-app
labels:
app: go-app
spec:
replicas: 3
template:
metadata:
labels:
app: go-app
spec:
containers:
- image: go-built-app:1.0
name: go-built-app
volumeMounts:
- name: my-host-path
mountPath: /go/src
volumes:
- name: my-host-path
hostPath:
path: /Users/shoeb240/go/src/github.com/shoeb240/go-in-kubernetes
type: DirectoryCreate docker image from Dockerfile
$ docker build -t go-built-app:1.0 .
Sending build context to Docker daemon 60.93kB
Step 1/11 : FROM golang:alpine AS builder
alpine: Pulling from library/golang
Digest: sha256:198cb8c94b9ee6941ce6d58f29aadb855f64600918ce602cdeacb018ad77d647
Status: Downloaded newer image for golang:alpine
---> f56365ec0638
Step 2/11 : ADD . /go/src/
---> c2fc6a922ba0
Step 3/11 : RUN apk add git
---> Running in 527f60150853
fetch http://dl-cdn.alpinelinux.org/alpine/v3.8/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/v3.8/community/x86_64/APKINDEX.tar.gz
(1/6) Installing nghttp2-libs (1.32.0-r0)
(2/6) Installing libssh2 (1.8.0-r3)
(3/6) Installing libcurl (7.61.1-r1)
(4/6) Installing expat (2.2.5-r0)
(5/6) Installing pcre2 (10.31-r0)
(6/6) Installing git (2.18.1-r0)
Executing busybox-1.28.4-r2.trigger
OK: 19 MiB in 20 packages
Removing intermediate container 527f60150853
---> 8855f35e2204
Step 4/11 : RUN git config --global core.autocrlf false
---> Running in a6630a8f9e41
Removing intermediate container a6630a8f9e41
---> 19e15d367f2b
Step 5/11 : RUN go get github.com/gorilla/mux
---> Running in 4174834b8f6e
Removing intermediate container 4174834b8f6e
---> 5d56aad41d92
Step 6/11 : WORKDIR /go/src
---> Running in 0f978cca307c
Removing intermediate container 0f978cca307c
---> baec6fad4026
Step 7/11 : RUN go build -o main .
---> Running in acb05153cb3c
Removing intermediate container acb05153cb3c
---> f668e9a60eb7
Step 8/11 : FROM alpine
latest: Pulling from library/alpine
Digest: sha256:46e71df1e5191ab8b8034c5189e325258ec44ea739bba1e5645cff83c9048ff1
Status: Downloaded newer image for alpine:latest
---> 3f53bb00af94
Step 9/11 : COPY --from=builder /go/src/main /app/
---> 7fc3723cd54a
Step 10/11 : WORKDIR /app
---> Running in be5f4e013dca
Removing intermediate container be5f4e013dca
---> 0a8db822adfe
Step 11/11 : CMD ["./main"]
---> Running in 81309e6bec41
Removing intermediate container 81309e6bec41
---> 2a34bf9f52fe
Successfully built 2a34bf9f52fe
Successfully tagged go-built-app:1.0
Check created docker images:
Shoeb-Mac:go-in-kubernetes shoeb240$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
go-built-app 1.0 2a34bf9f52fe 2 minutes ago 11.3MB
One of the most common Kubernetes object is the deployment object. The deployment object defines the container spec required, along with the name and labels used by other parts of Kubernetes to discover and connect to the application.
We will create container using image go-built-app in 3 pods.
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: go-app
labels:
app: go-app
spec:
replicas: 3
template:
metadata:
labels:
app: go-app
spec:
containers:
- image: go-built-app:1.0
name: go-built-app
volumeMounts:
- name: my-host-path
mountPath: /go/src
volumes:
- name: my-host-path
hostPath:
path: /Users/shoeb240/go/src/github.com/shoeb240/go-in-kubernetes
type: Directory
*Note: You must change spec.template.spec.volumes.hostPath.path according to your codebase absolute path.
Run kubectl command:
$ kubectl create -f deployment.yaml
deployment.extensions/go-app created
Checking deployment and service
$ kubectl get deployments
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
go-app 3 3 3 3 25s
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
go-app-5f55f4c977-6dkhr 1/1 Running 0 32s
go-app-5f55f4c977-6tg46 1/1 Running 0 32s
go-app-5f55f4c977-sprfb 1/1 Running 0 32s
Shoeb-Mac:go-in-kubernetes shoeb240$
We cannot yet access the app because port is not exposed outside world. We need to create service object for that.
Kubernetes has powerful networking capabilities that control how applications communicate. Service is assigned a unique IP address (also called clusterIP).
apiVersion: v1
kind: Service
metadata:
name: go-app-service
labels:
app: go-app
spec:
type: NodePort
ports:
- port: 8081
nodePort: 30081
selector:
app: go-app
Run kubectl command:
$ kubectl create -f service.yaml
service/go-app-service created
The Service selects all applications with the label go-app. As multiple replicas are deployed, they will be automatically load balanced based on this common label. The Service makes the application available via a NodePort.
Checking services
$ kubectl get service
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
go-app-service NodePort 10.109.45.113 <none> 8081:30081/TCP 7s
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 10d
Now we should be able to curl the go Service on :
$ curl localhost:30081/users
I am responding to your API call
We can scale up to 4 replicas from 3 modifying deployment.yaml replicas field as "replicas: 4" and running the following kubectl command
$ kubectl apply -f deployment.yaml
deployment.extensions/go-app configured
Lets check deployment and pods
$ kubectl get deployments
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
go-app 4 4 4 4 25m
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
go-app-5f55f4c977-6dkhr 1/1 Running 0 25m
go-app-5f55f4c977-6tg46 1/1 Running 0 25m
go-app-5f55f4c977-pzzfr 1/1 Running 0 41s
go-app-5f55f4c977-sprfb 1/1 Running 0 25m
Lets see how to find out problem when our deployment is not successful. For instance, we can put wrong image version in deployment.yaml. Our image version is 1.0, we can change it to 1.1 and create deployment again. Donot forget to delete previous deployment.
$ kubectl delete -f deployment.yaml
deployment.extensions "go-app" deleted
$ kubectl create -f deployment.yaml
deployment.extensions/go-app created
Checking deployment. We see that available deployment is 0.
$ kubectl get deployments
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
go-app 4 4 4 0 13s
Checking pods, they are not ready and status shows ErrImagePull and ImagePullBackOff. So we realize that we have issue with image.
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
go-app-56577bc9d4-8gmhc 0/1 ErrImagePull 0 21s
go-app-56577bc9d4-gbhkt 0/1 ImagePullBackOff 0 21s
go-app-56577bc9d4-lb9c7 0/1 ErrImagePull 0 21s
go-app-56577bc9d4-r5274 0/1 ErrImagePull 0 21s
To get more insight, we write command to describe pod
$ kubectl describe pod go-app-56577bc9d4-8gmhc
Name: go-app-56577bc9d4-8gmhc
Namespace: default
Node: docker-for-desktop/192.168.65.3
Start Time: Sun, 20 Jan 2019 22:04:45 +0600
Labels: app=go-app
pod-template-hash=1213367580
Annotations: <none>
Status: Pending
IP: 10.1.0.137
Controlled By: ReplicaSet/go-app-56577bc9d4
Containers:
go-built-app:
Container ID:
Image: go-built-app:1.1
Image ID:
Port: <none>
Host Port: <none>
State: Waiting
Reason: ImagePullBackOff
Ready: False
Restart Count: 0
Environment: <none>
Mounts:
/go/src from my-host-path (rw)
/var/run/secrets/kubernetes.io/serviceaccount from default-token-2q6zg (ro)
Conditions:
Type Status
Initialized True
Ready False
PodScheduled True
Volumes:
my-host-path:
Type: HostPath (bare host directory volume)
Path: /Users/shoeb240/go/src/github.com/shoeb240/go-in-kubernetes
HostPathType: Directory
default-token-2q6zg:
Type: Secret (a volume populated by a Secret)
SecretName: default-token-2q6zg
Optional: false
QoS Class: BestEffort
Node-Selectors: <none>
Tolerations: node.kubernetes.io/not-ready:NoExecute for 300s
node.kubernetes.io/unreachable:NoExecute for 300s
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled 103s default-scheduler Successfully assigned go-app-56577bc9d4-8gmhc to docker-for-desktop
Normal SuccessfulMountVolume 103s kubelet, docker-for-desktop MountVolume.SetUp succeeded for volume "my-host-path"
Normal SuccessfulMountVolume 103s kubelet, docker-for-desktop MountVolume.SetUp succeeded for volume "default-token-2q6zg"
Normal Pulling 43s (x3 over 101s) kubelet, docker-for-desktop pulling image "go-built-app:1.1"
Warning Failed 36s (x3 over 88s) kubelet, docker-for-desktop Failed to pull image "go-built-app:1.1": rpc error: code = Unknown desc = Error response from daemon: pull access denied for go-built-app, repository does not exist or may require 'docker login'
Warning Failed 36s (x3 over 88s) kubelet, docker-for-desktop Error: ErrImagePull
Normal BackOff 10s (x4 over 88s) kubelet, docker-for-desktop Back-off pulling image "go-built-app:1.1"
Warning Failed 10s (x4 over 88s) kubelet, docker-for-desktop Error: ImagePullBackOff
At the bottom of the output we see - Failed to pull image "go-built-app:1.1"