Tailing logs from CloudWatch for executed process

Author: meap

pkg/ecs/exec.go

@@ -122,6 +122,8 @@ func (s *Service) Execute(cmd []string, wait bool, dockerImageTag string) {
 		fmt.Printf("The task definition %s is used", taskDef)
 	}
 
+	fmt.Println()
+
 	output, err := svc.RunTask(ctx, &ecs.RunTaskInput{
 		Cluster:        &s.Cluster,
 		TaskDefinition: &taskDef,
@@ -146,24 +148,26 @@ func (s *Service) Execute(cmd []string, wait bool, dockerImageTag string) {
 	}
 
 	executedTask := output.Tasks[0]
+	var lastTimestamp *int64 = nil
+
+	fmt.Printf("Task %s executed", *executedTask.TaskArn)
+	fmt.Println()
 
-	log.Printf("Task %s executed", *executedTask.TaskArn)
 	if wait {
 		for {
+			logsOutput, _ := s.printProcessLogs(ctx, tdef.LogGroup, tdef.LogStreamPrefix, *executedTask.TaskArn, tdef.Name, lastTimestamp)
+			lastTimestamp = &logsOutput.lastEventTimestamp
+
 			success, err := s.wait(ctx, svc, *executedTask.TaskArn)
 			if err != nil {
-				logsErr := s.printProcessLogs(ctx, tdef.LogGroup, tdef.LogStreamPrefix, *executedTask.TaskArn, tdef.Name)
-				if logsErr != nil {
-					log.Printf("Failed to fetch events from CloudWatch %v", logsErr)
-				}
 				log.Fatalln(err)
 			}
 
 			if success {
 				break
 			}
 
-			time.Sleep(6 * time.Second)
+			time.Sleep(5 * time.Second)
 		}
 
 		fmt.Printf("task %s finished", *executedTask.TaskArn)

pkg/ecs/logs.go

@@ -3,39 +3,59 @@ package ecs
 import (
 	"context"
 	"fmt"
-	"log"
 
 	"github.com/aws/aws-sdk-go-v2/aws"
 	"github.com/aws/aws-sdk-go-v2/service/cloudwatchlogs"
 )
 
+type printProcessLogsOutput struct {
+	lastEventTimestamp int64
+}
+
 func (s *Service) printProcessLogs(
 	ctx context.Context, logGroupname string,
 	logStreamPrefix string,
 	taskArn string,
-	name string) error {
-	log.Printf("Loading logs for %s: %s", logGroupname, taskArn)
+	name string,
+	startTime *int64) (printProcessLogsOutput, error) {
 
 	cfg, err := s.initCfg()
 	if err != nil {
-		return fmt.Errorf("failed to initialize AWS configuration. (%w)", err)
+		return printProcessLogsOutput{}, fmt.Errorf("failed to initialize AWS configuration. (%w)", err)
 	}
 
 	processID := extractProcessID(taskArn)
 	client := cloudwatchlogs.NewFromConfig(cfg)
 
-	output, err := client.FilterLogEvents(ctx, &cloudwatchlogs.FilterLogEventsInput{
+	input := &cloudwatchlogs.FilterLogEventsInput{
 		LogGroupName:   aws.String(logGroupname),
 		LogStreamNames: []string{fmt.Sprintf("%s/%s/%s", logStreamPrefix, name, processID)},
-	})
+	}
+
+	if startTime != nil {
+		input.StartTime = startTime
+	}
+
+	output, err := client.FilterLogEvents(ctx, input)
 
 	if err != nil {
-		return fmt.Errorf("failed to filter log events (%w)", err)
+		return printProcessLogsOutput{}, fmt.Errorf("failed to filter log events (%w)", err)
 	}
 
 	for _, event := range output.Events {
 		fmt.Println(*event.LogStreamName, *event.Message)
 	}
 
-	return nil
+	var lastEventTimestamp int64
+	if len(output.Events) > 0 {
+		lastEventTimestamp = *output.Events[len(output.Events)-1].Timestamp + 1
+	} else if startTime != nil {
+		lastEventTimestamp = *startTime
+	} else {
+		lastEventTimestamp = 0
+	}
+
+	return printProcessLogsOutput{
+		lastEventTimestamp: lastEventTimestamp,
+	}, nil
 }