[chore][otel] Enable persistence in otel.yml

changelog/fragments/1726572104-enable-persistence-by-default.yaml

@@ -0,0 +1,32 @@
+# Kind can be one of:
+# - breaking-change: a change to previously-documented behavior
+# - deprecation: functionality that is being removed in a later release
+# - bug-fix: fixes a problem in a previous version
+# - enhancement: extends functionality but does not break or fix existing behavior
+# - feature: new functionality
+# - known-issue: problems that we are aware of in a given version
+# - security: impacts on the security of a product or a user’s deployment.
+# - upgrade: important information for someone upgrading from a prior version
+# - other: does not fit into any of the other categories
+kind: feature
+
+# Change summary; a 80ish characters long description of the change.
+summary: Enable persistence in the configuration provided with our OTeL distribution.
+
+# Long description; in case the summary is not enough to describe the change
+# this field accommodate a description without length limits.
+# NOTE: This field will be rendered only for breaking-change and known-issue kinds at the moment.
+#description:
+
+# Affected component; usually one of "elastic-agent", "fleet-server", "filebeat", "metricbeat", "auditbeat", "all", etc.
+component: elastic-agent,otel
+
+# PR URL; optional; the PR number that added the changeset.
+# If not present is automatically filled by the tooling finding the PR where this changelog fragment has been added.
+# NOTE: the tooling supports backports, so it's able to fill the original PR number instead of the backport PR number.
+# Please provide it if you are adding a fragment for a different PR.
+pr: 
+
+# Issue URL; optional; the GitHub issue related to this changeset (either closes or is part of).
+# If not present is automatically filled by the tooling with the issue linked to the PR number.
+#issue: https://github.com/owner/repo/1234

internal/pkg/otel/README.md

@@ -77,3 +77,35 @@ This section provides a summary of components included in the Elastic Distributi
 | Component | Version |
 |---|---|
 | [spanmetricsconnector](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/connector/spanmetricsconnector/v0.109.0/connector/spanmetricsconnector/README.md) | v0.109.0 |
+
+## Persistence in OpenTelemetry Collector
+
+By default, the OpenTelemetry Collector is stateless, which means it doesn't store offsets on disk while reading files. As a result, if you restart the collector, it won't retain the last read offset, potentially leading to data duplication or loss. However, we have configured persistence in the settings provided with the Elastic Agent package. 
+
+To enable persistence for the `filelogreceiver`, we add the `file_storage` extension and activate it for `filelog`. Here’s an example:
+
+```yaml
+receivers:
+  filelog/platformlogs:
+    include: [ /var/log/system.log ]
+    start_at: beginning
+    storage: file_storage/filelogreceiver
+extensions:
+  file_storage/filelogreceiver:
+    directory: ${env:STORAGE_DIR}
+exporters:
+  ...
+processors:
+  ...
+service:
+  extensions: [file_storage]
+  pipelines:
+    logs/platformlogs:
+      receivers: [filelog/platformlogs]
+      processors: [...]
+      exporters: [...]
+```
+
+> [!WARNING]  
+Removing the storage key from the filelog section will disable persistence, which will lead to data duplication or loss when the collector restarts.
+

otel.yml

@@ -2,6 +2,7 @@ receivers:
   filelog:
     include: [ /var/log/system.log ]
     start_at: beginning
+    storage: file_storage/filelogreceiver
 
 processors:
   resource:
@@ -24,6 +25,12 @@ extensions:
   health_check:
     endpoint: "localhost:13133"
     path: "/health/status"
+  file_storage/filelogreceiver:
+    create_directory: true
+
+    # RFC: The text below is just a placeholder. 
+    #      Please propose names for the default otel registry.
+    directory: ${env:STORAGE_DIR}
 
 service:
   extensions: [health_check, memory_limiter]