Policy Engine

As you build a design, Kanvas continuously evaluates the relationships between your components — to identify connections, validate them, and keep related configuration in sync. This page explains how you can choose which engine performs that evaluation, how to read the relationship indicator, and how to diagnose results that look wrong.

How Relationships Are Evaluated 🔗

Kanvas can run relationship evaluation using one of two interchangeable engines:

• Server-side – the policy engine running inside your Meshery server. It is always available.
• Client-side – the same policy engine, compiled to WebAssembly and run inside a background worker in your browser. Because it runs locally, there are no round-trips to the server, so evaluation is typically faster. A WASM evaluation times out after 10 seconds.

The default preference is Automatic, not the server. At load, Kanvas tries to start the WASM engine and waits up to 30 seconds for it to report ready. If it starts, WASM is used. If not, the Meshery server is used. Kanvas waits until changes stop for about one second, then evaluates. Another change during evaluation restarts the cycle. Evaluation runs after a configuration value or display name changes, a relationship is added or removed, a component is added, removed, duplicated, or merged, or a design loads or an import or merge completes.

Both engines produce the same relationship results. The choice affects performance, and where toil (evaluation) is done, not correctness.

Changing the Evaluation Engine Preference 🔗

The engine is controlled by the Relationship Evaluation Engine preference.

1. In Kanvas Designer, open Settings.
2. Find the Relationship Evaluation Engine preference.
3. Choose one of the following values:

The engine is selected once per session. Changing the preference takes full effect on the next session (for example, after reloading Kanvas).

Reading the Relationship Indicator 🔗

The relationship indicator tells you the state of the most recent evaluation:

• Evaluating — evaluation is in progress. This is normal after you add, remove, or reconfigure components.
• Evaluated — evaluation completed successfully and the relationships shown on the canvas are up to date. There is no error state on the indicator. A failed evaluation clears the last-evaluation details, so the tooltip returns to “No relationships evaluated yet”, and the failure is logged to the browser console only. Tooltips you will see: “Evaluating relationships…” while running, “Relationships evaluated” with the elapsed time when done, and “No relationships evaluated yet” when nothing has been evaluated. When Kanvas skips applying a result it shows “Skipping evaluation application”. A successful evaluation shows no message. WASM does not fall back to the server on its own after a fault.

What the one-time notifications mean 🔗

A failed evaluation does not raise an error state or a fallback notification. The failure is logged to the browser console only. If relationships stop updating, switch the engine to Meshery server and reload.

Diagnosing Failing or Unexpected Relationship Results 🔗

If relationships are missing or look wrong, turn on Enable Debugger in the Options dialog (it is off by default) and open the Evaluation Engine tab. Status reads Initialized, Not Initialized, or Not Available, plus the engine type WASM or SERVER. The tab refreshes every second. If WASM is not initialized, set the engine to Meshery server, reload, and compare.

Step 1 — Enable the debugger preference 🔗

The Diagnostics view is exposed under the Designer debugger preference.

1. In Kanvas Designer, open Settings.
2. Enable the debugger preference.
3. Open the Relationship Evaluation Diagnostics view.

Step 2 — Read the Diagnostics view 🔗

The Diagnostics view reports the current state of relationship evaluation:

• Status – Initialized, Not Initialized, or Not Available.
• Engine type – WASM or SERVER, plus any initialization error. The tab refreshes every second.
• There is no fallback counter. A runtime fault does not switch engines by itself.

Step 3 — Force the server engine if client results look wrong 🔗

If you suspect the client-side engine is producing incorrect results:

1. Open Settings.
2. Set Relationship Evaluation Engine to Meshery server.
3. Reload Kanvas so the new engine is used for the session.
4. Re-check the design’s relationships.

If the relationships are correct with the server engine but wrong with the client-side engine, that points to a client engine issue worth reporting (see below).

Step 4 — Re-trigger evaluation 🔗

Evaluation re-runs automatically whenever you change the design — for example, by adding, removing, or reconfiguring a component, or by toggling a relationship kind on or off from the Relationships section of the Designer. Making any such change re-triggers evaluation with the active engine. There is no error state for a successful re-evaluation to clear.

Step 5 — When and how to file a bug 🔗

If relationship results are still wrong or evaluation keeps failing after the steps above — especially if the Meshery server engine also produces incorrect or failing results — file a bug. Include the following from the Relationship Evaluation Diagnostics view so the issue can be reproduced:

• The engine type, WASM or SERVER, and any initialization error.
• The relationships you expected versus what Kanvas showed, and the design or a minimal version of it.

Related Reading

• Understanding Relationships
• Canvas Actions
• Cloning a Design
• Configuring Components
• Creating Relationships
• Deleting a Design

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