bd735de8c4
Add per-pattern message timeouts with sensible defaults (120s for deployments, 30s for queries/commands). Configure Akka.NET transport heartbeat explicitly rather than relying on framework defaults. Document per-site message ordering guarantee. Specify that in-flight messages on disconnect result in timeout error (no central buffering) and debug streams die on any disconnect.
48 lines
2.6 KiB
Markdown
48 lines
2.6 KiB
Markdown
# Communication Layer Refinement — Design
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**Date**: 2026-03-16
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**Component**: Central–Site Communication (`Component-Communication.md`)
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**Status**: Approved
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## Problem
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The Communication Layer doc defined 8 message patterns clearly but lacked specification for timeouts, transport configuration, reconnection behavior, message ordering guarantees, and connection failure handling.
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## Decisions
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### Message Timeouts
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- **Per-pattern timeouts with sensible defaults**, overridable in configuration.
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- Deployment and system-wide artifacts: 120 seconds (script compilation can be slow).
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- Lifecycle commands, integration routing, recipe/command delivery, remote queries: 30 seconds.
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- Uses the Akka.NET ask pattern; timeout results in failure to caller.
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### Transport Configuration
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- **Akka.NET built-in reconnection** with explicitly configured transport heartbeat interval and failure detection threshold.
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- No custom reconnection logic — framework handles it.
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- Settings explicitly documented rather than relying on framework defaults, for predictability in a SCADA context.
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### Connection Failure Behavior
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- **In-flight messages get a timeout error** — caller retries manually. No buffering at central. Consistent with existing design principle.
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- Automatic retry rejected due to risk of duplicate processing (e.g., site may have applied a deployment before the connection dropped).
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### Message Ordering
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- **Per-site ordering guaranteed** — relies on Akka.NET's built-in per-sender/per-receiver ordering. No custom sequencing logic needed.
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### Debug Stream Interruption
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- **Stream dies on any disconnect** (failover or network blip). Engineer reopens the debug view manually.
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- Auto-resume rejected — adds complexity for a transient diagnostic tool.
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## Affected Documents
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| Document | Change |
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|----------|--------|
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| `Component-Communication.md` | Added 4 new sections: Message Timeouts, Transport Configuration, Message Ordering, Connection Failure Behavior |
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## Alternatives Considered
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- **Global timeout for all patterns**: Rejected — deployment involves compilation and needs more time than a simple query.
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- **Default Akka.NET transport settings**: Rejected — relying on undocumented defaults is risky for SCADA; explicit configuration ensures predictable behavior.
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- **Automatic retry of in-flight messages**: Rejected — risks duplicate processing and contradicts the no-buffering-at-central principle.
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- **No ordering guarantee**: Rejected — Akka.NET provides this for free; the design already implicitly relies on it.
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- **Auto-resume debug streams on reconnection**: Rejected — adds state tracking complexity for a transient diagnostic feature.
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