K8s: Gate distributed component replicas on external datastore

[VietND96]

What

In distributed mode (isolateComponents: true), the Distributor, SessionQueue, and SessionMap components can be scaled to multiple replicas only when they share state through an external datastore (Redis/Postgres). This gates the replica count on that datastore so multi-replica setups without shared state can't be created by accident.

• Adds a seleniumGrid.component.replicaCount helper: it honors components.<x>.replicas when that component's externalDatastore.enabled is true, and otherwise forces 1 (nil-safe via dig).
• Uses it in the three distributed-mode deployments: distributor, session-queue, session-map.

Replica counts remain fully settable from chart values once a datastore is configured — this only prevents the silently-broken case of >1 replica with no shared state.

Why

Running multiple Distributor/SessionQueue/SessionMap replicas without a shared datastore breaks the grid (each replica has independent state). Previously replicas: {{ max 1 (...) }} allowed >1 regardless of datastore.

Verify

helm template with isolateComponents=true:

Scenario	distributor	session-queue	session-map
datastore ON, replicas 3/2/4	3	2	4
datastore OFF, replicas 3/2/4	1	1	1
mixed (only sessionMap datastore ON), all replicas=5	1	1	5

helm lint passes.

🤖 Generated with Claude Code

[qodo-code-review]

PR Summary by Qodo

Helm: Gate distributed component replica counts on external datastore

🐞 Bug fix ⚙️ Configuration changes 🕐 10-20 Minutes

AI Description

• Prevent Distributor/SessionQueue/SessionMap from scaling >1 without shared external state.
• Add a reusable Helm helper to compute safe replica counts per component.
• Apply the helper to distributed-mode deployments to avoid silently broken grids.

Diagram

graph TD
A["Chart values"] --> B["replicaCount helper"] --> C["Distributor deploy"]
B --> D["SessionQueue deploy"]
B --> E["SessionMap deploy"]
A --> F["externalDatastore.enabled"] --> B

Loading

High-Level Assessment

The following are alternative approaches to this PR:

1. Fail fast on invalid configuration (template error)

• ➕ Makes misconfiguration immediately visible during install/upgrade
• ➕ Avoids surprising behavior where user sets replicas>1 but gets 1
• ➖ Breaking/stricter behavior for existing users relying on current values
• ➖ Harder to support mixed scenarios unless error conditions are nuanced

2. Enforce via values.schema.json (JSON Schema validation)

• ➕ Validates early with clear, structured error messages
• ➕ Keeps templates simpler and shifts rules into schema
• ➖ Schema cannot always express cross-field constraints cleanly for per-component nesting
• ➖ Helm schema support varies by tooling; still may need template-side guards

3. Introduce a global 'distributedSharedStateRequired' toggle

• ➕ Explicit operator intent; avoids implicit gating
• ➕ Can be documented as a hard requirement for distributed mode
• ➖ Adds another knob and potential confusion
• ➖ Does not inherently prevent the broken state unless combined with validation

Recommendation: The implemented helper-based gating is a good default because it prevents the most harmful misconfiguration without breaking installs. If operators prefer strictness, consider a follow-up optional fail-fast mode (or schema validation) that errors when replicas>1 and externalDatastore is disabled, while keeping the current safe-default behavior as the baseline.

Files changed (4) +19 / -3

Bug fix (4) +19 / -3

_helpers.tplAdd helper to gate distributed component replica counts +16/-0

Add helper to gate distributed component replica counts

• Introduces a new Helm helper (seleniumGrid.component.replicaCount) that returns the configured replicas only when externalDatastore.enabled is true; otherwise forces replicas to 1. Uses dig for nil-safe access to nested values.

charts/selenium-grid/templates/_helpers.tpl

distributor-deployment.yamlUse gated replicaCount helper for Distributor deployment +1/-1

Use gated replicaCount helper for Distributor deployment

• Replaces the direct max(1, replicas) expression with the shared replicaCount helper so Distributor cannot scale beyond 1 without an external datastore.

charts/selenium-grid/templates/distributor-deployment.yaml

session-map-deployment.yamlUse gated replicaCount helper for SessionMap deployment +1/-1

Use gated replicaCount helper for SessionMap deployment

• Switches SessionMap replica calculation to the shared helper, allowing multi-replica only when its external datastore is enabled.

charts/selenium-grid/templates/session-map-deployment.yaml

session-queue-deployment.yamlUse gated replicaCount helper for SessionQueue deployment +1/-1

Use gated replicaCount helper for SessionQueue deployment

• Updates SessionQueue deployment to compute replicas via the shared helper, preventing multi-replica setups without shared external state.

charts/selenium-grid/templates/session-queue-deployment.yaml

[qodo-code-review]

Code Review by Qodo

🐞 Bugs (0) 📘 Rule violations (0) 📎 Requirement gaps (0)

Great, no issues found!

Qodo reviewed your code and found no material issues that require review