input: add new ring buffer metrics

When input plugins runs in threaded mode, they use a ring buffer to communicate with
the engine. This patch adds new metrics to track the behavior of the input ring buffer,
enabling better observability and troubleshooting in high-load or threaded environments.

The following counters are now registered per input instance:

  - fluentbit_input_ring_buffer_writes_total: Number of successful ring buffer writes
  - fluentbit_input_ring_buffer_retries_total: Number of retry attempts due to saturation
  - fluentbit_input_ring_buffer_retry_failures_total: Number of failed retries (after limit hit)

Example from Prometheus endpoint:

  # HELP fluentbit_input_ring_buffer_writes_total Number of ring buffer writes.
  # TYPE fluentbit_input_ring_buffer_writes_total counter
  fluentbit_input_ring_buffer_writes_total{name="syslog.0"} 15000

  # HELP fluentbit_input_ring_buffer_retries_total Number of ring buffer retries.
  # TYPE fluentbit_input_ring_buffer_retries_total counter
  fluentbit_input_ring_buffer_retries_total{name="syslog.0"} 820

  # HELP fluentbit_input_ring_buffer_retry_failures_total Number of ring buffer retry failures.
  # TYPE fluentbit_input_ring_buffer_retry_failures_total counter
  fluentbit_input_ring_buffer_retry_failures_total{name="syslog.0"} 5

Signed-off-by: Eduardo Silva <[email protected]>

Author: edsiper

include/fluent-bit/flb_input.h

@@ -426,6 +426,11 @@ struct flb_input_instance {
     struct cmt_counter *cmt_memrb_dropped_chunks;
     struct cmt_counter *cmt_memrb_dropped_bytes;
 
+    /* ring buffer 'write' metrics */
+    struct cmt_counter *cmt_ring_buffer_writes;
+    struct cmt_counter *cmt_ring_buffer_retries;
+    struct cmt_counter *cmt_ring_buffer_retry_failures;
+
     /*
      * Indexes for generated chunks: simple hash tables that keeps the latest
      * available chunks for writing data operations. This optimizes the

src/flb_input.c

@@ -1237,6 +1237,34 @@ int flb_input_instance_init(struct flb_input_instance *ins,
         cmt_counter_set(ins->cmt_memrb_dropped_bytes, ts, 0, 1, (char *[]) {name});
     }
 
+    /* fluentbit_input_ring_buffer_writes_total */
+    ins->cmt_ring_buffer_writes = \
+        cmt_counter_create(ins->cmt,
+                            "fluentbit", "input",
+                            "ring_buffer_writes_total",
+                            "Number of ring buffer writes.",
+                            1, (char *[]) {"name"});
+    cmt_gauge_set(ins->cmt_ring_buffer_writes, ts, 0, 1, (char *[]) {name});
+
+    /* fluentbit_input_ring_buffer_retries_total */
+    ins->cmt_ring_buffer_retries = \
+        cmt_counter_create(ins->cmt,
+                            "fluentbit", "input",
+                            "ring_buffer_retries_total",
+                            "Number of ring buffer retries.",
+                            1, (char *[]) {"name"});
+    cmt_counter_set(ins->cmt_ring_buffer_retries, ts, 0, 1, (char *[]) {name});
+
+
+    /* fluentbit_input_ring_buffer_retry_failures_total */
+    ins->cmt_ring_buffer_retry_failures = \
+        cmt_counter_create(ins->cmt,
+                            "fluentbit", "input",
+                            "ring_buffer_retry_failures_total",
+                            "Number of ring buffer retry failures.",
+                            1, (char *[]) {"name"});
+    cmt_counter_set(ins->cmt_ring_buffer_retry_failures, ts, 0, 1, (char *[]) {name});
+
     /* OLD Metrics */
     ins->metrics = flb_metrics_create(name);
     if (ins->metrics) {