Understand the wonderful use of dowanward API, and easily grasp kubernetes environment variables

introduction

Two days before , There is a new colleague in the company with a sad face , Looks preoccupied , I'll ask him what happened , It turned out that there was a demand that made it difficult ： Deploy four at a time pod, Every pod The name is not the same , How to judge which pod The generated logs ？ To hear that , I smile , Explained it to him Dowanward API The magic effect of , He listened to , The tight eyebrows slowly stretch out , I watched him write the name of the log as $MY_POD_NAME.log, I nodded my head gently to show my satisfaction . The promised weekend dinner party made me happy . Today will be Dowanward API To introduce the functions of .

General idea

By configuring environment variables or mounting Dowanward API In the form of a volume to expose pod Metadata , send pod Be able to obtain corresponding information .

Environmental preparation

1. Prepare three servers to build kubernetes colony .

The name of the node	IP
k8s-master	172.31.0.2
k8s-worker1	172.31.0.3
k8s-worker2	172.31.0.4

[[email protected] ~]# kubectl get nodes
NAME          STATUS   ROLES                  AGE    VERSION
k8s-master    Ready    control-plane,master   5d4h   v1.20.9
k8s-worker1   Ready    <none>                 5d4h   v1.20.9
k8s-worker2   Ready    <none>                 5d4h   v1.20.9
[[email protected] ~]# 

2. Get ready yaml To deploy the application .

# deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deploy
  namespace: default
  labels:
    app: nginx-deploy
spec:
  selector:
    matchLabels:
      app: nginx-deploy
  replicas: 4
  template:
    metadata:
      labels:
        app: nginx-deploy
    spec:
      containers:
        - name: mynginx
          image: nginx
          imagePullPolicy: IfNotPresent
          command: [ "/bin/bash", "-ce", "tail -f /dev/null" ]

test

Pass above deployment.yaml Deployed applications cannot be obtained pod Name , But use Dowanward API It can be done easily . There are two ways for your reference .

One 、 Configure environment variables

The above yaml To transform .

# deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deploy
  namespace: default
  labels:
    app: nginx-deploy
spec:
  selector:
    matchLabels:
      app: nginx-deploy
  replicas: 4
  template:
    metadata:
      labels:
        app: nginx-deploy
    spec:
      containers:
        - name: mynginx
          image: nginx
          imagePullPolicy: IfNotPresent
          command: [ "/bin/bash", "-ce", "tail -f /dev/null" ]
          env:
            - name: MY_POD_NAME
              valueFrom:
                fieldRef:
                  fieldPath: metadata.name
            - name: MY_POD_IP
              valueFrom:
                fieldRef:
                  fieldPath: status.podIP
            - name: HOST_IP
              valueFrom:
                fieldRef:
                  fieldPath: status.hostIP
            - name: LIMITS_MEMORY
              valueFrom:
                resourceFieldRef:
                  resource: limits.memory

We added environment variables env, Take... Separately pod Name and ip.

[[email protected] test]# kubectl apply -f deployment.yaml 
deployment.apps/nginx-deploy created
[[email protected] test]# kubectl get pod
NAME                            READY   STATUS    RESTARTS   AGE
nginx-deploy-6f4c989cff-2mcm5   1/1     Running   0          55s
nginx-deploy-6f4c989cff-mjx9n   1/1     Running   0          55s
nginx-deploy-6f4c989cff-vhncx   1/1     Running   0          56s
nginx-deploy-6f4c989cff-wtjzd   1/1     Running   0          57s
[[email protected] test]# 

Transformed yaml Successfully deployed 4 individual pod, We went inside the container to find out .

[[email protected] test]# kubectl exec -it nginx-deploy-6f4c989cff-2mcm5 -c mynginx -- /bin/bash
[email protected]:/# echo $MY_POD_NAME
nginx-deploy-6f4c989cff-2mcm5
[email protected]:/# echo $MY_POD_IP
192.168.126.42
[email protected]:/# echo $HOST_IP
172.31.0.4
[email protected]:/#

Successfully achieved pod Name and ip, And host ip You can also get , It can be used when writing code $MY_POD_NAME To get the corresponding value , Very flexible and convenient .

Two 、 mount Dowanward API volume

Or our initial deployment.yaml To transform .

# deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deploy
  namespace: default
  labels:
    app: nginx-deploy
spec:
  selector:
    matchLabels:
      app: nginx-deploy
  replicas: 4
  template:
    metadata:
      labels:
        app: nginx-deploy
    spec:
      containers:
      - image: nginx
        imagePullPolicy: IfNotPresent
        command: [ "/bin/bash", "-ce", "tail -f /dev/null" ]
        name: mynginx
        volumeMounts:
        - name: podinfo
          mountPath: /etc/podinfo
          readOnly: false
      volumes:
        - name: podinfo
          downwardAPI:
            items:
            - path: name
              fieldRef:
                fieldPath: metadata.name
            - path: namespace
              fieldRef:
                fieldPath: metadata.namespace

[[email protected] test]# kubectl apply -f deployment.yaml 
deployment.apps/nginx-deploy configured
[[email protected] test]# kubectl get pod
NAME                           READY   STATUS    RESTARTS   AGE
nginx-deploy-d5fc6886d-c7fvh   1/1     Running   0          4m8s
nginx-deploy-d5fc6886d-wgzvs   1/1     Running   0          4m6s
nginx-deploy-d5fc6886d-xc699   1/1     Running   0          4m6s
nginx-deploy-d5fc6886d-xvgj7   1/1     Running   0          4m8s
[[email protected] test]#

Also created 4 individual pod, We go inside the container .

[[email protected] test]# kubectl exec -it nginx-deploy-d5fc6886d-c7fvh -c mynginx -- /bin/bash
[email protected]:/# cd /etc/podinfo/
[email protected]:/etc/podinfo# ls
name  namespace
[email protected]:/etc/podinfo# cat name
nginx-deploy-d5fc6886d-c7fvh
[email protected]:/etc/podinfo# cat namespace 
default
[email protected]:/etc/podinfo# 

Also obtained pod name , But this method is not an environment variable , We need to do some processing when writing code .

It is recommended to use the form of configuring environment variables .

Sort out the summary

Dowanward API Common fields are as follows ：

1. Use fieldRef You can declare the fields used ：

full name	Age
spec.nodeName	Host name
status.hostIP	The host machine IP
metadata.name	Pod The name of
metadata.namespace	Pod Of Namespace
status.podIP	Pod Of IP
spec.serviceAccountName	Pod Of Service Account The name of
metadata.uid	Pod Of UID
metadata.labels['<KEY>']	Appoint <KEY> Of Label value
metadata.annotations['<KEY>']	Appoint <KEY> Of Annotation value
metadata.labels	Pod All of the Label
metadata.annotations	Pod All of the Annotation

2. Use resourceFieldRef You can declare the fields used ：

full name	Age
limits.cpu	Container of CPU limit
requests.cpu	Container of CPU request
limits.memory	Container of memory limit
requests.memory	Container of memory request

This paper is written by mdnice Multi platform Publishing