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Checks Package

The checks package provides CEL (Common Expression Language) expression evaluation for health check validation. It is used by providers to validate responses and resources using powerful, flexible expressions.

Debugging CEL Expressions

Use ph context to inspect the evaluation context available to your CEL expressions:

# View context for a configured component
ph context my-app

# View context for ad-hoc provider
ph context kubernetes --kind deployment --namespace default --name my-app

# Output as YAML for readability
ph context my-app -o yaml

CEL Expression Syntax

CEL expressions must evaluate to a boolean (true for healthy, false for unhealthy). Expressions have access to provider-specific context variables (e.g., response for HTTP, resource for Kubernetes).

Check Modes

Each check can optionally specify a mode field:

  • default (no mode field): The expression is evaluated once against the full provider context.
  • mode: "each": The expression is evaluated per-item for providers that return collections (e.g., Kubernetes with label selectors). Each item is evaluated independently, and failures reference the specific item.
checks:
  - check: "resource.status.readyReplicas >= resource.spec.replicas"
    message: "Not all replicas ready"
    mode: "each"

Built-in Functions

The following custom functions are available in all CEL expressions:

  • time.Now() - Returns the current timestamp
  • time.Since(timestamp) - Returns the duration elapsed since the given timestamp
  • time.Until(timestamp) - Returns the duration until the given timestamp
checks:
  - check: "time.Until(tls.validUntil) > duration('168h')"
    message: "Certificate expires within 7 days"

Standard Extensions

The following CEL extension libraries are available:

  • Strings: Additional string functions (charAt, indexOf, replace, split, substring, trim, upperAscii, lowerAscii)
  • Lists: List manipulation functions (slice, flatten)
  • Encoders: Base64 encoding/decoding (base64.encode, base64.decode)
  • Math: Math functions (math.greatest, math.least)
  • Sets: Set operations (sets.contains, sets.intersects, sets.equivalent)
  • Bindings: Variable binding via cel.bind()

Common CEL Patterns

Note: The examples below use data as a generic illustrative placeholder variable. Actual CEL context variables are provider-specific — for example, response for HTTP, resource for Kubernetes, tls for TLS, health for Vault, and release/chart for Helm. See each provider's README for its available CEL variables, or use ph context to inspect the evaluation context.

Simple Field Validation

checks:
  - check: "data.ready == true"
    message: "Service not ready"

Nested Field Access

checks:
  - check: "data.services.database.connected == true"
    message: "Database not connected"

Numeric Comparisons

checks:
  - check: "data.activeConnections < 1000"
    message: "Too many active connections"

Array Operations

checks:
  - check: "size(data.errors) == 0"
    message: "System has reported errors"
  - check: "size(data.items) > 0"
    message: "No items in response"

String Operations

checks:
  - check: 'data.message.contains("SUCCESS")'
    message: "Success message not found"
  - check: 'data.version.startsWith("2.")'
    message: "Wrong API version"

Logical Operations

checks:
  - check: "data.value >= 200 && data.value < 300"
    message: "Value outside expected range"
  - check: 'data.state == "active" || data.state == "standby"'
    message: "Service in unexpected state"

Regex Pattern Matching

checks:
  - check: 'data.id.matches("\\d{3}-\\d{2}-\\d{4}")'
    message: "Invalid format in response"
  - check: 'data.status.matches("(?i)success|ok|healthy")'
    message: "No success indicator found"

Existence Checks (Lists)

checks:
  - check: "data.conditions.exists(c, c.type == 'Ready' && c.status == 'True')"
    message: "Ready condition not met"

Map Key Checks

checks:
  - check: "'required_key' in data.config"
    message: "Required key missing from config"

Security

  • CEL expressions are validated at configuration load time to catch syntax errors early
  • CEL expressions are sandboxed and cannot execute arbitrary code or access the filesystem
  • Expression evaluation is deterministic and side-effect free