1# Google App Engine to Azure App Service Migration
2 
3Detailed guidance for migrating Google App Engine applications to Azure App Service.
4 
5## Service Mapping
6 
7| GCP Service | Azure Equivalent |
8|-------------|------------------|
9| App Engine (Standard) | Azure App Service (Standard/Premium plan) |
10| App Engine (Flex) | Azure App Service (Premium v3) or Container Apps |
11| App Engine Services | App Service apps (one per service) |
12| `app.yaml` | `azure.yaml` + Bicep |
13| Datastore / Firestore | Azure Cosmos DB |
14| Cloud SQL (PostgreSQL) | Azure Database for PostgreSQL Flexible Server |
15| Cloud SQL (MySQL) | Azure Database for MySQL Flexible Server |
16| Cloud Storage | Azure Blob Storage |
17| Cloud Tasks | Azure Service Bus / Durable Functions |
18| Cloud Pub/Sub | Azure Service Bus / Event Grid |
19| Memcache / Memorystore | Azure Cache for Redis |
20| Cloud Scheduler | Azure Functions Timer trigger |
21| Cloud CDN | Azure Front Door / Azure CDN |
22| Cloud DNS | Azure DNS |
23| Cloud Logging | Application Insights / Azure Monitor |
24| Cloud Monitoring | Azure Monitor Metrics |
25| Cloud Trace | Application Insights (distributed tracing) |
26| Cloud IAM | Managed Identity + Azure RBAC |
27| Cloud Build | GitHub Actions / Azure DevOps |
28| Traffic Splitting | Deployment Slots (weighted routing) |
29| Service Versions | Deployment Slots |
30| Cloud KMS | Azure Key Vault |
31| Secret Manager | Azure Key Vault |
32| Cloud Endpoints | Azure API Management |
33| Identity-Aware Proxy | Azure Front Door + Entra ID auth |
34| VPC Connector | VNet Integration |
35 
36## Standard vs Flex → App Service Plan Mapping
37 
38| App Engine Tier | App Service Equivalent | Notes |
39|-----------------|------------------------|-------|
40| Standard (F1 instance) | Free (F1) | Dev/test only |
41| Standard (B1/B2) | Basic (B1/B2) | Low-traffic apps |
42| Standard (auto-scaling) | Standard (S1-S3) | Auto-scale, slots |
43| Flex (custom runtime) | Premium v3 (P1v3-P3v3) | Custom containers |
44| Flex (high-memory) | Premium v3 (P3v3) | Up to 32 GB RAM |
45 
46## `app.yaml` → `azure.yaml` + Bicep
47 
48### App Engine Configuration Mapping
49 
50| `app.yaml` Field | Azure Equivalent | Implementation |
51|-------------------|------------------|----------------|
52| `runtime: python312` | Runtime stack: Python 3.12 | Bicep `siteConfig.linuxFxVersion` |
53| `instance_class: F2` | App Service Plan SKU | Bicep `sku.name` |
54| `automatic_scaling` | Autoscale settings | Bicep `Microsoft.Insights/autoscalesettings` |
55| `env_variables` | App Settings | Bicep `siteConfig.appSettings` |
56| `handlers` (URL routing) | App Service path mappings / Front Door | Route rules |
57| `entrypoint` | Startup command | `az webapp config set --startup-file` |
58| `vpc_access_connector` | VNet Integration | Bicep `virtualNetworkSubnetId` |
59| `inbound_services: [warmup]` | Always On | Bicep `siteConfig.alwaysOn: true` |
60 
61### Example: `app.yaml` → Bicep
62 
63```yaml
64# app.yaml (GCP)
65runtime: python312
66instance_class: F2
67automatic_scaling:
68  min_instances: 1
69  max_instances: 10
70env_variables:
71  DATABASE_URL: "postgres://..."
72```
73 
74```bicep
75// Bicep equivalent
76resource appServicePlan 'Microsoft.Web/serverfarms@2023-12-01' = {
77  sku: { name: 'S2', capacity: 1 }
78  properties: { reserved: true }
79}
80 
81resource webApp 'Microsoft.Web/sites@2023-12-01' = {
82  properties: {
83    siteConfig: {
84      linuxFxVersion: 'PYTHON|3.12'
85      alwaysOn: true
86      appSettings: [
87        { name: 'PGHOST', value: postgresServer.properties.fullyQualifiedDomainName }
88      ]
89    }
90  }
91}
92```
93 
94## Datastore / Firestore → Cosmos DB
95 
96| Datastore Feature | Cosmos DB Equivalent |
97|-------------------|----------------------|
98| Entity / Document | Item |
99| Kind / Collection | Container |
100| Namespace | Database |
101| Key / ID | Partition key + ID |
102| Ancestor queries | Hierarchical partition keys |
103| Eventual consistency | Session or Eventual consistency |
104| Strong consistency | Strong consistency |
105| `ndb` / `google.cloud.datastore` | `@azure/cosmos` SDK |
106 
107> 💡 **Tip:** Use Cosmos DB for NoSQL API for the closest mapping from Datastore. Use Cosmos DB for MongoDB API if the app already uses MongoDB-compatible patterns.
108 
109## Cloud Tasks → Service Bus / Durable Functions
110 
111| Cloud Tasks Feature | Azure Equivalent |
112|--------------------|------------------|
113| HTTP target tasks | Service Bus + Azure Functions |
114| App Engine target tasks | Service Bus + WebJobs |
115| Task scheduling (delayed) | Service Bus scheduled messages |
116| Task retry / dead-letter | Service Bus retry + dead-letter queue |
117| Rate limiting | Service Bus message throttling |
118| Task orchestration | Durable Functions (fan-out/fan-in) |
119 
120## Traffic Splitting → Deployment Slots
121 
122| App Engine Feature | Azure Equivalent |
123|--------------------|------------------|
124| Version traffic splitting (%) | Slot traffic routing (%) |
125| Canary deployment | Slot with low traffic % |
126| A/B testing | Slot traffic routing |
127| Version rollback | Slot swap (revert) |
128| Gradual rollout | Increase slot traffic % incrementally |
129| Warmup requests | Slot warm-up (pre-swap) |
130 
131```bicep
132// Configure traffic routing: 90% production, 10% staging
133resource siteConfig 'Microsoft.Web/sites/config@2023-12-01' = {
134  name: 'web'
135  properties: {
136    experiments: {
137      rampUpRules: [{
138        actionHostName: '${webApp.name}-staging.azurewebsites.net'
139        reroutePercentage: 10
140        name: 'staging'
141      }]
142    }
143  }
144}
145```
146 
147## Memcache → Azure Cache for Redis
148 
149| Memcache Feature | Azure Cache for Redis |
150|------------------|----------------------|
151| `memcache.get()` / `set()` | `redis.get()` / `redis.set()` |
152| Shared memcache | Azure Cache for Redis (Basic) |
153| Dedicated memcache | Azure Cache for Redis (Standard/Premium) |
154| Session store | Redis session store |
155| Cache expiry | Redis TTL |
156 
157## Environment Variables Migration
158 
159| Source | Target | Notes |
160|--------|--------|-------|
161| `app.yaml` env_variables | App Settings | Non-sensitive config |
162| Secret Manager refs | Key Vault references | `@Microsoft.KeyVault(SecretUri=...)` |
163| Runtime env (auto-injected) | App Settings | Map GAE-specific vars |
164| `GAE_APPLICATION` | `WEBSITE_SITE_NAME` | Auto-injected by App Service |
165| `PORT` | `PORT` | Auto-injected by App Service |
166| `GOOGLE_CLOUD_PROJECT` | (no equivalent) | GCP project IDs identify a runtime environment; Azure subscription IDs are a tooling/billing context, not a runtime equivalent. Use App Service `WEBSITE_RESOURCE_GROUP` or rely on `DefaultAzureCredential` to discover the subscription at runtime if needed. |
167 
168## CI/CD Migration
169 
170| Cloud Build / gcloud | Azure Equivalent |
171|---------------------|------------------|
172| `gcloud app deploy` | `az webapp deploy` or `azd deploy` |
173| `cloudbuild.yaml` | `.github/workflows/deploy.yml` |
174| Cloud Build triggers | GitHub Actions triggers |
175| Artifact Registry | Azure Container Registry |
176| `gcloud app versions` | Deployment slots |
177 
178## Reference Links
179 
180- [GCP to Azure services comparison](https://learn.microsoft.com/en-us/azure/architecture/gcp-professional/)
181- [App Service overview](https://learn.microsoft.com/en-us/azure/app-service/overview)
182- [Cosmos DB migration options](https://learn.microsoft.com/en-us/azure/cosmos-db/migration-choices)
183- [App Service deployment slots](https://learn.microsoft.com/en-us/azure/app-service/deploy-staging-slots)
184