Introduction

IBM Fusion Backup and Restore recipes have a decision-making field called "condition" within the check hooks. The result obtained from evaluating this field determines the outcome of the hook. Therefore, it is important to write the "condition" string carefully, ensuring that it is valid and recognized by the recipe on the cluster.

Over time, these check hooks have been enhanced to support logical expression evaluation, enabling more complex conditions to be defined in a structured and intuitive manner.

In this article, will explore how to write the "condition" field effectively, with clarity and fair understanding.

What is the format for Check Hook “condition” string?

At minimum, it includes two JSONPath expressions enclosed in curly braces and separated by an operator.

Condition string = {expression1} <operator> {expression2}

Expression1 and Expression2

Should be valid JSONPath expressions, representing either a namespace-scoped or cluster-scope Kubernetes resource.

Operator

It can be one of the below comparison operators:

• ==
• !=
• <
• >
• <=
• >=

Note: In Fusion 2.9, check with logical expressions was introduced. Allowing users to have multiple logical expressions in check hooks using AND ( && ) and OR ( || ) operators. It is also possible to create complex groupings using parentheses. Few valid examples are:

{$.spec.replicas} == {$.status.readyReplicas}

{$.spec.replicas} == {$.status.readyReplicas} || {$.metadata.generation} == {$.status.observedGeneration} && {$.spec.progressDeadlineSeconds} == {"500"}

({$.spec.replicas} == {$.status.readyReplicas}) || (({$.metadata.generation} == {$.status.observedGeneration}) && {$.spec.progressDeadlineSeconds} == {"500"}

Order of evaluation

Firstly, JSONPath expressions are evaluated, followed by inner groups present in the parentheses and then any outer groups. If logical groups are at same level, then they will be evaluated from left to right.

Write a condition string

Let’s quickly write condition string for Db2uCluster resource status. Snippet below shows its status details.

    "status": {
        "conditions": [
            {
                "lastTransitionTime": "2025-03-26T10:31:21Z",
                "status": "OK",
                "type": "FormationStatus"
            }
        ],
        "maintenanceState": "InMaintenance",
        "state": "Ready",
        "version": "s11.5.9.0"
    }

Say – We want to validate for its “Ready” state?
For this, check hook condition can be written as –

      chks:
        - condition: '{$.status.state} == {"Ready"}'

      chks:
        - condition: '({$.status.state} == {"Ready"}) && ({$.status.conditions[?(@.type=="FormationStatus")].status} == {"OK"})'

      chks:
        - condition: '(({$.status.state} == {"Ready"}) && ({$.status.conditions[?(@.type=="FormationStatus")].status} == {"OK"}))'

  hooks:
  - name: db2uclusters-check
    labelSelector: for-backup=true
    namespace: ${GROUP.db2u-volumes.namespace}
    selectResource: db2u.databases.ibm.com/v1/db2uclusters
    timeout: 300
    type: check
    chks:
    - condition: '(({$.status.state} == {"Ready"}) && ({$.status.conditions[?(@.type=="FormationStatus")].status} == {"OK"}))'
      name: stateReady
      onError: fail
      timeout: 300
    onError: fail