Implement Client Migration Strategy - The Migrator

Implementation

Migrating clients from API v1 to v2 should be gradual and safe. Canary deployments start with a small percentage of traffic; a/b testing routes specific users deterministically; tracking migration progress shows when it is safe to fully sunset v1.

Implement a node that manages client migration across API versions:

// Canary at 10%: most traffic stays on v1
{ "type": "get_users", "msg_id": 1, "user_id": "user123" }
{ canary_percentage: 10 }
-> { "type": "users_response", "in_reply_to": 1,
    "version": "v1", "canary": false }

// 50/50 traffic split
{ "type": "get_users", "msg_id": 2 }
{ traffic_split: {"v1": 50, "v2": 50} }
-> { "type": "users_response", "in_reply_to": 2,
    "version": "<v1 or v2>" }

// Track how many clients have migrated
{ "type": "get_migration_stats", "msg_id": 3 }
-> { "type": "migration_stats", "in_reply_to": 3,
    "total_clients": 1000,
    "version_percentages": {"v1": 20, "v2": 80},
    "migration_complete": false }

// Gradual rollout with health checks between steps
{ "type": "gradual_rollout", "msg_id": 4,
  "steps": [{"percentage":10,"duration_minutes":60},
              {"percentage":50,"duration_minutes":240}] }
-> { "type": "rollout_complete", "in_reply_to": 4,
    "final_percentage": 50, "health_checks_passed": true }

Sample Test Cases

Canary deployment routingTimeout: 5000ms

Input

{
  "src": "client",
  "dest": "api",
  "body": {
    "type": "get_users",
    "msg_id": 1,
    "user_id": "user123"
  },
  "canary_percentage": 10
}

Expected Output

{"type": "users_response", "in_reply_to": 1, "version": "v1", "canary": false}

Traffic splittingTimeout: 5000ms

Input

{
  "src": "client",
  "dest": "api",
  "body": {
    "type": "get_users",
    "msg_id": 1
  },
  "traffic_split": {
    "v1": 50,
    "v2": 50
  }
}

Expected Output

{"type": "users_response", "in_reply_to": 1, "version": ".*"}

Hints

Hint 1▾

Canary: route 10% of traffic to v2 (hash user_id % 100 < 10); rest to v1

Hint 2▾

Traffic split: use a random number per request and route by bucket percentage

Hint 3▾

migration stats: count requests by version over time; migration_complete when v1 usage drops to 0

Hint 4▾

Gradual rollout: each step increases the v2 percentage after checking health metrics

Hint 5▾

health_checks_passed: true means no error rate increase was detected during rollout

Implementation

Sample Test Cases

Hints

Resources

Theoretical Hub

Key Concepts