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Hot Reload
Zero-downtime schema updates
Hot reloading enables the router to update its supergraph schema without restarting, providing zero-downtime schema updates.
Before enabling hot reload, consult the support matrix to ensure your schema source is supported, and carefully consider the performance considerations.
Hot reload support matrix
| Schema Source | Hot Reload Support | Notes |
|---|---|---|
| Apollo Uplink | 🟢 Yes | Automatically polls every 10 seconds for updates |
| Local file | 🟢 Yes | Requires --hot-reload flag or APOLLO_ROUTER_HOT_RELOAD=true |
| Remote URLs | ❌ No | Schema fetched once at startup |
Performance considerations
When using hot reloading for supergraph schemas, be aware of the following performance considerations:
Schema reloading overhead: Each schema reload requires parsing and validation, which temporarily increases CPU usage.
Request handling: During reload, new requests might experience slight latency increases while the new schema is being processed.
Memory usage: The router maintains both the old and new schema briefly during reload, temporarily increasing memory usage.
Configure reload retries
When a reload fails — for example, because a transient network error prevents the router from fetching a persisted query manifest from Uplink — the router automatically retries instead of continuing to serve traffic on the previous configuration indefinitely.
Tune this behavior with the reload configuration section:
1reload:
2 # Maximum number of retry attempts after a failed reload.
3 # 0 disables automatic retries. null allows unlimited retries.
4 # Default: 5
5 max_retries: 5
6
7 # Base delay between retry attempts. A random jitter of up to 25% is added
8 # to spread retries across multiple router instances.
9 # Default: 10s
10 retry_delay: 10sThe retry budget is reset whenever the router receives a new reload trigger — a new schema or license from Uplink, a configuration or rhai script file change, or an explicit reload signal — so any new change will always get a fresh set of attempts even if previous retries were exhausted.
Production recommendations
For production deployments with high traffic:
Monitor during reloads: If using hot reload, monitor CPU, memory, and latency metrics during schema updates.
Schedule updates: Plan schema updates during lower-traffic periods when using hot reload.
Use blue/green deployments: For production deployments requiring schema updates, use blue/green deployment strategies with OCI digest references.