How can I make the shell evaluate a filename argument in a Kubernetes CronJob?-CodePudding

I have the following CronJob to run a backup of my database, and I'd like the backup files to be appended with the date:

{{- if .Values.postgresqlBackup.enabled }}
apiVersion: batch/v1
kind: CronJob
metadata:
  name: postgres-backup
spec:
  schedule: {{ .Values.postgresqlBackup.cron | quote }}
  jobTemplate:
    spec:
      template:
        spec:
          containers:
            - name: postgres
              image: postgres:latest
              imagePullPolicy: IfNotPresent
              command: 
                - pg_dump 
                - --username=postgres 
                - --no-password
                - --format=custom
                - --file=/backups/dragalia-api-$(date  "%Y-%m-%d_%H-%M-%S").bak
                - --host={{ include "dragalia-api.fullname" . }}-postgresql
                - --verbose
              volumeMounts:
                - name: data
                  mountPath: /backups
              env:
                - name: PGPASSWORD
                  valueFrom:
                    secretKeyRef:
                      name: {{ include "dragalia-api.fullname" . }}-postgresql
                      key: postgres-password
                      optional: false
          restartPolicy: Never
          volumes:
            - name: data
              persistentVolumeClaim:
                claimName: {{ include "dragalia-api.fullname" . }}-db-backup
{{- end }}

The job executes successfully but I am left with files like:

docker@minikube:/dragalia-api/db-backup$ ls
'dragalia-api-$(date  "%Y-%m-%d_%H-%M-%S").bak'

The entire filename is quoted and the string is not evaluated. How can I make it so that the string is evaluated by the shell?

Things I've tried:

using backticks: --file=/backups/dragalia-api-1`date "%Y-%m-%d_%H-%M-%S".bak` : still rendered literally
defining a DATE env var and putting ${DATE} in the string: rendered literally
escaping the % signs e.g. \%Y: rendered literally
passing a multi-line string to sh -c: this caused the job to fail on being unable to connect to the db, so I guess --host was not passed properly

The only other thing I can think of is passing in a shell script, but I'd rather not create another resource if possible.

Equivalently, since the date information is stored by the filesystem, if there's some other way to pass a unique string into the filename that would work. Anything so that it keeps rolling backups instead of just the one.

CodePudding user response：

If you want to use shell substitution, then you need to execute your command with a shell. For example:

containers:
  - name: postgres
    image: postgres:latest
    imagePullPolicy: IfNotPresent
    command:
      - /bin/sh
      - -c
      - >
        pg_dump
        --username=postgres
        --no-password
        --format=custom
        --file=/backups/dragalia-api-$(date  "%Y-%m-%d_%H-%M-%S").bak
        --host={{ include "dragalia-api.fullname" . }}-postgresql
        --verbose

Also, unrelated to your question, you should pin your postgres image to a specific version (postgres:14) or you'll be in for a rude surprise when :latest is unexpectedly a new major version.

CodePudding user response：

... if there's some other way to pass a unique string into the filename ...

If you don't actually care about the format of the filename, you can use the container name. The CronJob creates a sequence of Job objects, but each will have a different name indirectly based on the execution time (also see Predictable pod name in kubernetes cron job). The Job name will become the Pod name; then you can use the downward API to get that into an environment variable; and then you can substitute environment variables into the command without a shell.

containers:
  - name: postgres
    image: postgres:latest
    env:
      - name: PGPASSWORD
        valueFrom: {...}
      - name: POD_NAME
        valueFrom:
          fieldRef:
            fieldPath: metadata.name
    command: 
      - pg_dump
      - ...
      - --file=/backups/dragalia-api-$(POD_NAME).bak
      - ...

Your current filename format will almost certainly be easier to read and manage, but this particular invocation at least doesn't require invoking a shell.