Add retry with exponential backoff to HTTP client

- Add retry_max_attempts, retry_initial_delay_ms, retry_max_delay_ms, retry_backoff_multiplier to config
- Retry on network failures, 5xx errors, 429 (rate limit), 408 (timeout)
- No retry on 4xx client errors or user interrupt (Sysbreak)
- Default: 3 attempts, 100ms initial delay, 5s max delay, 2x multiplier
- Uses existing IO.sleep_s from generic_io

src/client/exporter_config.ml

@@ -33,6 +33,10 @@ type t = {
   batch_timeout_ms: int;
   self_trace: bool;
   http_concurrency_level: int option;
+  retry_max_attempts: int;
+  retry_initial_delay_ms: float;
+  retry_max_delay_ms: float;
+  retry_backoff_multiplier: float;
   _rest: rest;
 }
 
@@ -82,6 +86,10 @@ let pp out (self : t) : unit =
     batch_logs;
     batch_timeout_ms;
     http_concurrency_level;
+    retry_max_attempts;
+    retry_initial_delay_ms;
+    retry_max_delay_ms;
+    retry_backoff_multiplier;
     _rest = _;
   } =
     self
@@ -95,13 +103,16 @@ let pp out (self : t) : unit =
      %a@];@ protocol=%a;@ timeout_ms=%d;@ timeout_traces_ms=%d;@ \
      timeout_metrics_ms=%d;@ timeout_logs_ms=%d;@ batch_traces=%a;@ \
      batch_metrics=%a;@ batch_logs=%a;@ batch_timeout_ms=%d;@ \
-     http_concurrency_level=%a @]}"
+     http_concurrency_level=%a;@ retry_max_attempts=%d;@ \
+     retry_initial_delay_ms=%.0f;@ retry_max_delay_ms=%.0f;@ \
+     retry_backoff_multiplier=%.1f @]}"
     debug pp_log_level log_level sdk_disabled self_trace url_traces url_metrics
     url_logs ppheaders headers ppheaders headers_traces ppheaders
     headers_metrics ppheaders headers_logs pp_protocol protocol timeout_ms
     timeout_traces_ms timeout_metrics_ms timeout_logs_ms ppiopt batch_traces
     ppiopt batch_metrics ppiopt batch_logs batch_timeout_ms ppiopt
-    http_concurrency_level
+    http_concurrency_level retry_max_attempts retry_initial_delay_ms
+    retry_max_delay_ms retry_backoff_multiplier
 
 let default_url = "http://localhost:4318"
 
@@ -128,6 +139,10 @@ type 'k make =
   ?batch_timeout_ms:int ->
   ?self_trace:bool ->
   ?http_concurrency_level:int ->
+  ?retry_max_attempts:int ->
+  ?retry_initial_delay_ms:float ->
+  ?retry_max_delay_ms:float ->
+  ?retry_backoff_multiplier:float ->
   'k
 
 module type ENV = sig
@@ -234,7 +249,8 @@ module Env () : ENV = struct
       ?(timeout_ms = get_timeout_from_env "OTEL_EXPORTER_OTLP_TIMEOUT" 10_000)
       ?timeout_traces_ms ?timeout_metrics_ms ?timeout_logs_ms
       ?(batch_timeout_ms = 2_000) ?(self_trace = false) ?http_concurrency_level
-      =
+      ?(retry_max_attempts = 3) ?(retry_initial_delay_ms = 100.)
+      ?(retry_max_delay_ms = 5000.) ?(retry_backoff_multiplier = 2.0) =
     let url_traces, url_metrics, url_logs =
       let base_url =
         let base_url =
@@ -333,6 +349,10 @@ module Env () : ENV = struct
         batch_timeout_ms;
         self_trace;
         http_concurrency_level;
+        retry_max_attempts;
+        retry_initial_delay_ms;
+        retry_max_delay_ms;
+        retry_backoff_multiplier;
         _rest = ();
       }
 end

src/client/exporter_config.mli

@@ -88,6 +88,15 @@ type t = {
           be used to represent the size of a pool of workers where each worker
           gets a batch to send, send it, and repeats.
           @since NEXT_RELEASE *)
+  retry_max_attempts: int;
+      (** Maximum number of retry attempts for failed exports. 0 means no retry,
+          1 means one retry after initial failure. Default 3. *)
+  retry_initial_delay_ms: float;
+      (** Initial delay in milliseconds before first retry. Default 100ms. *)
+  retry_max_delay_ms: float;
+      (** Maximum delay in milliseconds between retries. Default 5000ms. *)
+  retry_backoff_multiplier: float;
+      (** Multiplier for exponential backoff. Default 2.0. *)
   _rest: rest;
 }
 (** Configuration.
@@ -123,6 +132,10 @@ type 'k make =
   ?batch_timeout_ms:int ->
   ?self_trace:bool ->
   ?http_concurrency_level:int ->
+  ?retry_max_attempts:int ->
+  ?retry_initial_delay_ms:float ->
+  ?retry_max_delay_ms:float ->
+  ?retry_backoff_multiplier:float ->
   'k
 (** A function that gathers all the values needed to construct a {!t}, and
     produces a ['k]. ['k] is typically a continuation used to construct a

src/client/generic_http_consumer.ml

@@ -62,6 +62,13 @@ end = struct
 
     let send (self : t) (sigs : OTEL.Any_signal_l.t) : (unit, error) result IO.t
         =
+      let should_retry = function
+        | `Failure _ -> true (* Network errors, connection issues *)
+        | `Status (code, _) ->
+          (* Retry on server errors, rate limits, timeouts *)
+          code >= 500 || code = 429 || code = 408
+        | `Sysbreak -> false (* User interrupt, don't retry *)
+      in
       let res = Resource_signal.of_signal_l sigs in
       let url, signal_headers =
         match res with
@@ -78,6 +85,30 @@ end = struct
       in
       let headers = List.rev_append signal_headers filtered_general in
       let data = Resource_signal.Encode.any ~encoder:self.encoder res in
+
+      (* Retry loop with exponential backoff *)
+      let rec retry_send attempt delay_ms =
+        let open IO in
+        let* result =
+          Httpc.send self.http ~url ~headers ~decode:(`Ret ()) data
+        in
+        match result with
+        | Ok x -> return (Ok x)
+        | Error err
+          when should_retry err && attempt < self.config.retry_max_attempts ->
+          let delay_s = delay_ms /. 1000. in
+          let* () = sleep_s delay_s in
+          let next_delay =
+            min self.config.retry_max_delay_ms
+              (delay_ms *. self.config.retry_backoff_multiplier)
+          in
+          retry_send (attempt + 1) next_delay
+        | Error _ as err -> return err
+      in
+
+      if self.config.retry_max_attempts > 0 then
+        retry_send 0 self.config.retry_initial_delay_ms
+      else
         Httpc.send self.http ~url ~headers ~decode:(`Ret ()) data
   end