feat: add Lambda SnapStart support#790
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Switch from the git-branch dependency to the published lambda_http/lambda_runtime 1.3.0 from crates.io, removing the release blocker. Also fix the integration test body-reader helpers to accept the BoxBody response type, and resolve a clippy ok().expect() lint.
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| import os | |||
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Summary
Adds AWS Lambda SnapStart support to the Lambda Web Adapter. Because the adapter runs the customer's web application as a separate process with no access to the Lambda Runtime API, the application cannot participate in the SnapStart lifecycle on its own. This PR makes the adapter a SnapStart bridge: it registers the runtime's
SnapStartResourcehooks and relays the before-checkpoint and after-restore lifecycle events to the inner application over HTTP.What it does
Two opt-in, independent environment variables:
AWS_LWA_SNAPSTART_BEFORE_CHECKPOINT_PATHAWS_LWA_SNAPSTART_AFTER_RESTORE_PATHafter_restore()performs three ordered steps (before any invocation is served):OnceLock) so it never reuses a connection captured in the snapshot — this happens first so the hook call itself uses a fresh connection.Each hook POST is bounded by a 60s timeout; the post-restore readiness check is bounded by a tighter 10s timeout. A non-2xx, connection error, or timeout at any step fails the SnapStart phase (
/init/errorfor before-checkpoint,/restore/errorfor after-restore) rather than serving traffic against an improperly restored app.Security: the hook routes live on the app's HTTP surface, so external requests (via API Gateway/ALB) targeting a configured hook path receive
403 Forbiddenand are never forwarded to the app.Behavior is unchanged when SnapStart is not in use — the runtime lifecycle is a no-op, and the hooks are unset by default. The previous
pool_max_idle_per_host(0)SnapStart special-case is removed in favor of the at-restore client swap, which restores connection pooling for steady-state throughput.Notable implementation details
lambda_http/lambda_runtime1.3.0 (adds theSnapStartResourceAPI).fetch_responsereturn type changed toResponse<BoxBody<Bytes, Error>>so the synthetic 403 can share the return type with proxied responses.readiness.rs, reused by both the adapter and the after-restore step.Testing
connection_id; the failure path (unready app) times out the readiness check at ~10s and fails the restore withSnapStartTimeoutException.cargo test,cargo clippy --all-targets -- -Dwarnings, andcargo fmt --checkall pass.Examples
Two deployable examples:
examples/fastapi-snapstart(container image / OCI) andexamples/fastapi-snapstart-zip(managed runtime layer), each demonstrating connection drain/reconnect across a restore.