[cmd/opampsupervisor]: do not log err when last received doesn't exist (

open-telemetry#36014)

.chloggen/36014_do_not_log_when_no_prev_config_exists.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: cmd/opampsupervisor
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Do not log err if the last received doesn't exist
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [36013]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

cmd/opampsupervisor/supervisor/supervisor.go

@@ -782,15 +782,18 @@ func (s *Supervisor) loadAndWriteInitialMergedConfig() error {
 	if s.config.Capabilities.AcceptsRemoteConfig {
 		// Try to load the last received remote config if it exists.
 		lastRecvRemoteConfig, err = os.ReadFile(filepath.Join(s.config.Storage.Directory, lastRecvRemoteConfigFile))
-		if err == nil {
+		switch {
+		case err == nil:
 			config := &protobufs.AgentRemoteConfig{}
 			err = proto.Unmarshal(lastRecvRemoteConfig, config)
 			if err != nil {
 				s.logger.Error("Cannot parse last received remote config", zap.Error(err))
 			} else {
 				s.remoteConfig = config
 			}
-		} else {
+		case errors.Is(err, os.ErrNotExist):
+			s.logger.Info("No last received remote config found")
+		default:
 			s.logger.Error("error while reading last received config", zap.Error(err))
 		}
 	} else {