queue collector exports on disk and retry without a time limit

nix/otel-export-queue.nix

@@ -0,0 +1,27 @@
+# Export settings every forwarding exporter in this tree attaches, imported by
+# both collector tiers (`host-modules/otel.nix`, `host-modules/swarm-otel.nix`).
+#
+# `sending_queue.storage` puts the queue on the `file_storage` extension, so
+# batches waiting for an exporter survive a collector restart. The journald
+# receiver saves its cursor before it hands an entry on: an entry sitting in an
+# in-memory queue when the exporter's target is down or the collector restarts
+# counts as consumed and is not read again.
+#
+# `queue_size` counts requests (batches), not records. When the queue is full
+# the exporter refuses new data and logs the drop; the oldest queued batches
+# are kept.
+#
+# `max_elapsed_time = "0s"` retries a failing batch until it is accepted.
+# The queue bound is what limits the disk used; the default of five minutes
+# gives up on a backlog that a store restart outlasts.
+{
+  sending_queue = {
+    enabled = true;
+    storage = "file_storage";
+    queue_size = 5000;
+  };
+  retry_on_failure = {
+    enabled = true;
+    max_elapsed_time = "0s";
+  };
+}