Architecture Upgrade Program (Modular Monolith First)

Last Updated: 2026-02-28
Audience: Engineering leads, backend/frontend engineers, release owners
Status: Completed baseline program (feature-freeze track)

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Objective

Upgrade the existing system architecture to align with industry best practices for:

• scalability
• flexibility
• operational reliability
• performance
• maintainability

while intentionally pausing net-new features until architecture foundations are stable.

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Target Direction

Use a Modular Monolith as the primary architecture target before any microservice split.

Why this direction:

• lower operational complexity than early microservices
• faster stabilization and refactor velocity
• cleaner boundaries and dependency control
• easier testing and observability rollout
• preserves optional future extraction paths

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Program Phases

Phase 0: Architecture Freeze + Baseline (current)

Scope

• Freeze net-new features (except critical security/bug fixes).
• Establish baseline metrics and current-state architecture inventory.
• Identify boundary smells, duplicate paths, and high-risk coupling.

Deliverables

• As-is architecture map and domain inventory
• Ranked flaw list (severity + impact + migration risk)
• Baseline metric capture method (latency, errors, queue, test reliability, env drift)
• No-feature execution checklist

Exit Criteria

• Baseline report published and accepted
• Top architecture risks explicitly prioritized
• Owners assigned for first structural refactor wave

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Phase 1: Target Architecture + Standards

Scope

• Define target modular blueprint (C4-lite + module boundaries).
• Define mandatory architecture standards and rules.

Mandatory Standards

• one canonical runtime path per concern
• strict typed config contract (env validation is single source)
• explicit contracts at boundaries (schema-first I/O)
• observability-by-default for critical operations
• deprecation policy and ADR-first architecture decisions

Deliverables

• target module boundary map
• architecture rulebook
• dependency direction rules
• refactor acceptance gates

Exit Criteria

• Rulebook approved
• module boundary ADR accepted
• migration sequence locked for Phase 2

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Phase 2: Structural Refactor (2–4 weeks)

Scope

• Restructure into clear domains (chat/runtime/tools/memory/queue/auth/protocols/files).
• Remove overlapping runtime paths and dead compatibility branches.
• Enforce dependency direction (core domains must not depend on adapters/infrastructure).

Deliverables

• module-by-module refactor PR sequence
• anti-drift tests for boundary import constraints
• reduced cross-domain coupling in orchestration layer

Exit Criteria

• circular dependency risk removed from critical paths
• documented canonical path for runtime/tool/queue
• anti-drift checks passing in release gate

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Phase 3: Reliability + Performance Hardening (parallel)

Scope

• Stabilize observability and SLO-oriented operations.
• Profile and optimize top bottlenecks.

Deliverables

• per-stage latency visibility with stable interpretation
• queue backlog and failure visibility
• tool denial visibility by reason and protocol context
• baseline SLO targets and error budget draft
• bottleneck optimization backlog (DB, queue throughput, prompt/runtime overhead)

Exit Criteria

• operational diagnosis possible without code spelunking
• performance baseline and target deltas documented

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Phase 4: Release Governance + Future-Proofing

Scope

• Lock architecture discipline into release process.
• Prepare future extraction seams without premature service split.

Deliverables

• mandatory curated release gate usage
• architecture guard checks in CI
• future extraction playbook (criteria-based, not trend-based)

Exit Criteria

• governance checks enforced consistently
• extraction criteria documented for future scale events

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Target End-State Criteria ("Good Enough to Scale")

The architecture is considered foundation-ready when all are true:

• clear domain boundaries with no critical circular dependencies
• single canonical path for runtime orchestration, tool execution, and queue behavior
• curated release gate stable with low flakiness
• typed config convergence with controlled/explicit drift
• observability sufficient for incident diagnosis without reading source code
• SLO-aligned performance under expected load profiles

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Execution Policy

• No feature work unless security-critical or production-critical.
• All architecture-affecting changes must update:
  • closure done-definition
  • release-gate evidence
  • relevant ADR/rule docs
• Every refactor PR must include:
  • boundary impact summary
  • migration safety note
  • gate test evidence

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Completion Update (2026-02-28)

• Phase 0: Completed (audit + baseline published)
• Phase 1: Completed (rulebook + anti-drift checks active)
• Phase 2: Completed (direct aso.service imports removed from runtime paths; facades enforce canonical access)
• Phase 3: Completed (runtime observability snapshot and runbook operationalized)
• Phase 4: Completed (curated release gate + architecture guard checks documented/enforced)

Program now shifts from migration mode to maintenance mode:

• keep feature-freeze discipline for architecture-sensitive changes
• enforce anti-drift and release-gate checks on every high-impact PR