gcp-to-aws

What this skill does

# GCP-to-AWS Migration Skill

## Philosophy

- **Re-platform by default**: Select AWS services that match GCP workload types (e.g., Cloud Run → Fargate, Cloud SQL → RDS).
- **Dev sizing unless specified**: Default to development-tier capacity (e.g., db.t4g.micro, single AZ). Upgrade only on user direction.
- **No human one-time migration costs**: Do not present human labor, professional services, or people-time work as dollar estimates or "one-time migration cost" budget categories. Vendor charges grounded in data (for example GCP data transfer egress in the infra estimate when billing exists) are allowed.
- **Multi-signal approach**: Design phase adapts based on available inputs — Terraform IaC for infrastructure, billing data for service mapping, and app code for AI workload detection.
- **BigQuery / `google_bigquery_*`**: The skill **does not** recommend a specific AWS analytics or warehouse service. During **Clarify**, if discovery shows BigQuery (IaC `google_bigquery_*` and/or billing rows for BigQuery), you **must** surface the specialist advisory **before** Design (see `references/phases/clarify/clarify.md`). Design output uses **`Deferred — specialist engagement`**; keep directing the user to their **AWS account team** and/or a **data analytics migration partner** through Design, Estimate, and docs (see `references/phases/design/design-infra.md` BigQuery specialist gate).

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## Definitions

- **"Load"** = Read the file using the Read tool and follow its instructions. Do not summarize or skip sections.
- **`$MIGRATION_DIR`** = The run-specific directory under `.migration/` (e.g., `.migration/0226-1430/`). Set during Phase 1 (Discover).

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## Context Loading Rules

Each phase loads reference files on demand. To keep per-turn context manageable and prevent instruction-following degradation:

- **Budget:** Each phase should load no more than ~800 lines of instructions (excluding user artifacts like JSON profiles and MCP tool results).
- **Conditional loading:** Reference files with trigger conditions (e.g., `agentic_profile.is_agentic == true`) MUST NOT be loaded unless the condition is met. Do not speculatively load files.
- **No duplication:** Model mapping tables, pricing data, and shared warnings exist in one canonical file. Other files reference them; they do not copy them inline.
- **Progressive depth:** Phase orchestrators (`design.md`, `generate.md`) contain short routing logic that points to detailed sub-files. Load the sub-file only when its path is selected.

**Conditional reference files (load ONLY when condition is true):**

| File                                             | Condition                                                                                          |
| ------------------------------------------------ | -------------------------------------------------------------------------------------------------- |
| `design-refs/ai-gemini-to-bedrock.md`            | `ai-workload-profile.json` exists AND `summary.ai_source` = `"gemini"` or `"both"`                 |
| `design-refs/ai-openai-to-bedrock.md`            | `ai-workload-profile.json` exists AND `summary.ai_source` = `"openai"` or `"both"`                 |
| `design-refs/ai.md`                              | `ai-workload-profile.json` exists AND `summary.ai_source` = `"other"`                              |
| `design-refs/design-ref-harness.md`              | `agentic_profile.is_agentic == true` AND `ai_constraints.agentic.migration_approach == "harness"`  |
| `design-refs/design-ref-agentic-to-agentcore.md` | `agentic_profile.is_agentic == true` AND `ai_constraints.agentic.migration_approach == "strands"`  |
| `shared/retarget-gotchas.md`                     | `agentic_profile.is_agentic == true` AND `ai_constraints.agentic.migration_approach == "retarget"` |

When adding new reference files, verify the phase's total loaded instructions remain under budget. If a new file would exceed ~800 lines when combined with other loaded refs, split it or make it conditional.

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## Prerequisites

User must provide at least one GCP source:

- **Terraform IaC**: `.tf` files (with optional `.tfvars`, `.tfstate`)
- **Application code**: Source files with GCP SDK or AI framework imports
- **Billing data**: GCP billing/cost/usage export files (CSV or JSON)

If none of the above are found, stop and ask user to provide at least one source type.

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## State Machine

This is the execution controller. After completing each phase, consult this table to determine the next action.

| Current State | Condition                                                             | Next Action                                                                            |
| ------------- | --------------------------------------------------------------------- | -------------------------------------------------------------------------------------- |
| `discover`    | `phases.discover != "completed"`                                      | Load `references/phases/discover/discover.md`                                          |
| `clarify`     | `phases.discover == "completed"` AND `phases.clarify != "completed"`  | Load `references/phases/clarify/clarify.md`                                            |
| `design`      | `phases.clarify == "completed"` AND `phases.design != "completed"`    | Load `references/phases/design/design.md`                                              |
| `estimate`    | `phases.design == "completed"` AND `phases.estimate != "completed"`   | Load `references/phases/estimate/estimate.md`                                          |
| `generate`    | `phases.estimate == "completed"` AND `phases.generate != "completed"` | Load `references/phases/generate/generate.md`                                          |
| `complete`    | `phases.generate == "completed"` AND `phases.feedback == "pending"`   | Set `phases.feedback` to `"completed"` (user had two chances), then migration complete |
| `complete`    | `phases.generate == "completed"` AND `phases.feedback == "completed"` | Migration planning complete                                                            |

**How to determine current state (deterministic):**

1. Read `$MIGRATION_DIR/.phase-status.json`
2. If `current_phase` exists, use it (must match one of: discover, clarify, design, estimate, generate, complete)
3. Otherwise use ordered phase evaluation: `discover` → `clarify` → `design` → `estimate` → `generate`
4. Pick the **first** phase in that order where `phases.<phase> != "completed"`; if none, state is `complete`

**Phase gate checks**: If prior phase incomplete, do not advance (e.g., cannot enter estimate without completed design).

**Clarify is mandatory:** Do not load `references/phases/design/design.md`, `references/phases/estimate/estimate.md`, or `references/phases/generate/generate.md` unless `$MIGRATION_DIR/.phase-status.json` exists and `phases.clarify` is exactly `"completed"`. A `preferences.json` file alone is **not** sufficient proof that Clarify ran. If the user asks to skip Clarify or jump straight to Design, cost estimate, or artifact generation, refuse briefly, then load `references/phases/clarify/clarify.md` and run Phase 2. There is no exception for "quick" or "obvious" migrations.

**Feedback checkpoints**: Feedback is not a sequential phase — it is offered at two interleaved checkpoints (after Discover and after Estimate). See the **Feedback Checkpoints** section below for details.

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## State Validation

When reading `$MIGRATION_DIR/.phase-status.json`, validate before proceeding:

1. **Multiple sessions**: If multiple directories exist under `.migration/`, list them with their phase status and ask: [A] Resume latest, [B] Start fresh, [C] Cancel.
2. **Invalid JSON**: If `.phase-status.json` fails to parse, STOP. Output: "State file corrupted (invalid JSON). Delete the file and restart the current phase."
3. **Unrecognized phase**: If `phases` object contains a phase not in {discove