Support one-shot agent execution mode (#6150)

This supports the use case of having the agent itself be ephemeral, which may be useful in various situations, including use of the local backend.

Co-authored-by: Max Anurin <theanurin@gmail.com>
Co-authored-by: qwerty287 <80460567+qwerty287@users.noreply.github.com>
Co-authored-by: 6543 <6543@obermui.de>

cmd/agent/core/agent.go

@@ -90,7 +90,14 @@ func run(ctx context.Context, c *cli.Command, backends []types.Backend) error {
 		hostname, _ = os.Hostname()
 	}
 
-	counter.Polling = c.Int("max-workflows")
+	maxWorkflows := c.Int("max-workflows")
+	singleWorkflow := c.Bool("single-workflow")
+	if singleWorkflow && maxWorkflows > 1 {
+		log.Warn().Msgf("max-workflows forced from %d to 1 due to agent running single workflow mode.", maxWorkflows)
+		maxWorkflows = 1
+	}
+
+	counter.Polling = maxWorkflows
 	counter.Running = 0
 
 	if c.Bool("healthcheck") {
@@ -201,8 +208,6 @@ func run(ctx context.Context, c *cli.Command, backends []types.Backend) error {
 	}
 	log.Debug().Msgf("loaded %s backend engine", backendEngine.Name())
 
-	maxWorkflows := c.Int("max-workflows")
-
 	customLabels := make(map[string]string)
 	if err := stringSliceAddToMap(c.StringSlice("labels"), customLabels); err != nil {
 		return err
@@ -298,6 +303,11 @@ func run(ctx context.Context, c *cli.Command, backends []types.Backend) error {
 
 				log.Debug().Msg("polling new workflow")
 				if err := runner.Run(agentCtx, shutdownCtx); err != nil {
+					if singleWorkflow {
+						log.Error().Err(err).Msg("runner done with error")
+						ctxCancel(nil)
+						return nil
+					}
 					log.Error().Err(err).Msg("runner error, retrying...")
 					// Check if context is canceled
 					if agentCtx.Err() != nil {
@@ -311,13 +321,23 @@ func run(ctx context.Context, c *cli.Command, backends []types.Backend) error {
 						// Continue to next iteration
 					}
 				}
+
+				if singleWorkflow {
+					log.Info().Msg("shutdown single workflow runner")
+					ctxCancel(nil)
+					return nil
+				}
 			}
 		})
 	}
 
-	log.Info().Msgf(
-		"starting Woodpecker agent with version '%s' and backend '%s' using platform '%s' running up to %d pipelines in parallel",
-		version.String(), backendEngine.Name(), engInfo.Platform, maxWorkflows)
+	log.Info().
+		Str("version", version.String()).
+		Str("backend", backendEngine.Name()).
+		Str("platform", engInfo.Platform).
+		Int("parallel workflows", maxWorkflows).
+		Bool("single workflow", singleWorkflow).
+		Msg("starting Woodpecker agent")
 
 	return serviceWaitingGroup.Wait()
 }

cmd/agent/core/flags.go

@@ -77,6 +77,12 @@ var flags = []cli.Flag{
 		Usage:   "agent parallel workflows",
 		Value:   1,
 	},
+	&cli.BoolFlag{
+		Sources: cli.EnvVars("WOODPECKER_AGENT_SINGLE_WORKFLOW"),
+		Name:    "single-workflow",
+		Usage:   "exit the agent after first workflow",
+		Value:   false,
+	},
 	&cli.BoolFlag{
 		Sources: cli.EnvVars("WOODPECKER_HEALTHCHECK"),
 		Name:    "healthcheck",