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Matthew Holt 2022-07-10 23:29:59 -06:00
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@ -255,7 +255,7 @@ Caddy's config API provides [ACID guarantees](https://en.wikipedia.org/wiki/ACID
For example, two clients may `GET /config/foo` at the same time, make an edit within that scope (config path), then call `POST|PUT|PATCH|DELETE /config/foo/...` at the same time to apply their changes, resulting in a collision: either one will overwrite the other, or the second might leave the config in an unintended state since it was applied to a different version of the config than it was prepared against. This is because the changes are not aware of each other.
Caddy's API does not support transactions spanning multiple requests, and HTTP is a stateless protocol. However, you can use the `Etag` trailer and `If-Match` header to detect and prevent collisions for any and all changes as a kind of pessimistic concurrency control. This is useful if there is any chance that you are using Caddy's `/config/...` endpoints concurrently without synchronization. All responses to `GET /config/...` requests have an HTTP trailer called `Etag` that contains the path and a hash of the contents in that scope (e.g. `Etag: "/config/apps/http/servers 65760b8e"`). Simply set the `If-Match` header on a mutative request to that of an Etag trailer from a previous `GET` request.
Caddy's API does not support transactions spanning multiple requests, and HTTP is a stateless protocol. However, you can use the `Etag` trailer and `If-Match` header to detect and prevent collisions for any and all changes as a kind of optimistic concurrency control. This is useful if there is any chance that you are using Caddy's `/config/...` endpoints concurrently without synchronization. All responses to `GET /config/...` requests have an HTTP trailer called `Etag` that contains the path and a hash of the contents in that scope (e.g. `Etag: "/config/apps/http/servers 65760b8e"`). Simply set the `If-Match` header on a mutative request to that of an Etag trailer from a previous `GET` request.
The basic algorithm for this is as follows: