Limits
Numeric limits and timeouts for serverlets, proxies, and DNS.
Technical limits and timeouts enforced by the platform. Most applications never hit these — they exist to keep the platform stable under load and to catch misbehaving configuration early.
Serverlet
| Limit | Value |
|---|---|
| Max instances per serverlet | 1,000 |
| Max container image size | 3 GiB |
| Scale-to-zero cold start timeout | 20 seconds |
| Rolling update grace period | 10 seconds |
If a serverlet with zero running instances receives a request, the proxy waits up to the cold start timeout for an instance to start before giving up and returning 504 Gateway Timeout. See Scaling to zero.
During a rolling update, an outgoing instance is given the grace period to finish in-flight requests before it’s stopped, regardless of whether it’s done.
Proxy
Request and response limits
| Limit | Value |
|---|---|
| Max request header size | 64 KB |
| Max response header size | 128 KB |
| Max size of a single header field | 32 KB |
| Max number of headers | 500 |
Timeouts
| Timeout | Value |
|---|---|
| Connect timeout to backend | 10 seconds |
| Time waiting for backend to start responding | 30 seconds |
| Overall backend request timeout | 100 seconds |
| Idle connection timeout to backend | 90 seconds |
| Idle timeout on HTTP/3 (QUIC) connections | 30 seconds |
| Response write timeout | 30 seconds |
Recursion
| Limit | Value |
|---|---|
| Max times a request can re-enter the platform | 3 |
A request can be forwarded back into the Futrou platform at most this many times before it’s rejected with 508 Loop Detected — this catches misconfigured proxies that end up routing to themselves, directly or indirectly. A proxy target that resolves back to the exact same instance already handling the request is blocked outright, regardless of this count.
Reserved headers
Request and response headers starting with Futrou- are reserved for platform use. Rules can’t add or modify a Futrou--prefixed header.
DNS
| Limit | Value |
|---|---|
| Max records per zone | 3,500 |
| Max zone size | 2 MiB |
Whichever of these two limits is reached first applies. See DNS for supported record types and zone management.
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