Implement feature request: To detect duplicate defined environment variables

[ryo-yamaoka]

score/container: To detect duplicate defined environment variables.

Fixes #448

behaviour

$ ./kube-score score ~/test.yaml 
apps/v1/Deployment sample-deployment                                          💥
    [CRITICAL] Environment Variable Key Duplication
        · sampleA -> Environment Variable Key Duplication
            Container environment variable key 'SAMPLE_ENV_VAR' duplicated
        · sampleB -> Environment Variable Key Duplication
            Container environment variable key 'SAMPLE_ENV_VAR1' duplicated
        · sampleB -> Environment Variable Key Duplication
            Container environment variable key 'SAMPLE_ENV_VAR2' duplicated

apiVersion: apps/v1
kind: Deployment
metadata:
  name: sample-deployment
  labels:
    app: sample
  annotations:
    kube-score/ignore: pod-networkpolicy,container-resources,container-image-pull-policy,container-security-context-privileged,container-security-context-user-group-id,container-security-context-readonlyrootfilesystem,container-ephemeral-storage-request-and-limit,container-image-tag
spec:
  replicas: 1
  selector:
    matchLabels:
      app: sample
  template:
    metadata:
      labels:
        app: sample
    spec:
      containers:
      - name: sampleA
        image: sample:latest
        ports:
        - containerPort: 80
        env:
        - name: SAMPLE_ENV_VAR
          value: sample1
        - name: SAMPLE_ENV_VAR
          value: sample1
      - name: sampleB
        image: sample:latest
        ports:
        - containerPort: 80
        env:
        - name: SAMPLE_ENV_VAR1
          value: sample1
        - name: SAMPLE_ENV_VAR1
          value: sample1
        - name: SAMPLE_ENV_VAR2
          value: sample2
        - name: SAMPLE_ENV_VAR2
          value: sample2

[ryo-yamaoka]

@zegl @atombrella Thanks for review, I fixed those.

[bors[bot]]

Build succeeded:

• ci/circleci: test