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Fix AWS ECS Task Stuck in Pending State

Resolve ECS tasks stuck in PENDING state by diagnosing resource constraints, networking issues, and task definition problems.

Published: Apr 1, 20266 min readBy FixWikiHub Editorial Team

Abstract illustration for a troubleshooting knowledge base category.

Introduction

ECS tasks in PENDING state are scheduled but haven't transitioned to RUNNING. The task has been placed on a container instance, but something is preventing the container from starting. Tasks stuck in PENDING indicate a launch or configuration problem.

Symptoms

```bash $ aws ecs describe-tasks --cluster my-cluster --tasks abc123 --query 'tasks[*].[lastStatus,stoppedReason]'

[["PENDING", null]] ```

In the ECS console, the task shows:

bash

Status: PENDING
(Details tab shows no containers started)

Common Causes

1.Insufficient resources - Instance lacks CPU, memory, or network ports
2.Image pull failure - Container image doesn't exist, access denied, or timeout
3.Network configuration - Incorrect VPC, subnets, or security groups
4.IAM role issues - Task execution role missing or insufficient permissions
5.Task definition errors - Invalid container definition
6.Container instance issues - Docker daemon problems on the host
7.EFS mount failures - EFS volume can't be mounted
8.Startup dependency failure - Init container or dependency not ready

Step-by-Step Fix

1.Check logs for specific error messages
2.Verify configuration settings
3.Test network connectivity
4.Review recent changes
5.Apply corrective action
6.Verify the fix

Step 1: Check Task Details and Stopped Reason

bash

aws ecs describe-tasks --cluster my-cluster --tasks abc123 \
  --query 'tasks[*].[lastStatus,stoppedReason,containers[*].reason]'

If the task eventually stops, check the reason:

bash

aws ecs describe-tasks --cluster my-cluster --tasks abc123 \
  --query 'tasks[*].stoppedReason'

Common stopped reasons: - Resource is no longer able to be provisioned - Task failed to start - CannotPullContainerError: access denied - CannotPullContainerError: registry timeout

Step 2: Check Container Instance Resources

For EC2 launch type:

```bash # Get the container instance ID aws ecs describe-tasks --cluster my-cluster --tasks abc123 \ --query 'tasks[*].containerInstanceArn'

# Check instance resources aws ecs describe-container-instances \ --cluster my-cluster \ --container-instances arn:aws:ecs:region:account:container-instance/my-cluster/abc123 \ --query 'containerInstances[*].[remainingResources,broadcastChannelArn]' ```

Look at remaining CPU and memory. If insufficient:

bash

# Add more instances to the cluster
aws autoscaling set-desired-capacity \
  --auto-scaling-group-name my-asg \
  --desired-capacity 5

For Fargate, check if you have service quotas:

bash

aws service-quotas get-service-quota \
  --service-code fargate \
  --quota-code L-3032A538  # Fargate On-Demand resource count

Step 3: Check Container Image Access

```bash # Get image from task definition aws ecs describe-task-definition --task-definition my-task:1 \ --query 'taskDefinition.containerDefinitions[*].image'

# Test image pull manually (on EC2 instance) docker pull nginx:latest ```

For ECR images, verify permissions:

```bash # Check if task execution role can pull from ECR aws ecr describe-repositories --repository-names my-repo

# Verify ECR policy allows pull aws ecr get-repository-policy --repository-name my-repo ```

Task execution role needs:

json

{
  "Effect": "Allow",
  "Action": [
    "ecr:GetAuthorizationToken",
    "ecr:BatchCheckLayerAvailability",
    "ecr:GetDownloadUrlForLayer",
    "ecr:BatchGetImage"
  ],
  "Resource": "*"
}

Step 4: Check Network Configuration

bash

aws ecs describe-tasks --cluster my-cluster --tasks abc123 \
  --query 'tasks[*].attachments[*].details'

Verify: - Subnets exist and are in the same VPC - Security groups allow necessary traffic - For Fargate, subnets must have internet access (NAT gateway) or VPC endpoints

Test connectivity:

bash

# Run a test task to check connectivity
aws ecs run-task \
  --cluster my-cluster \
  --task-definition debug-task \
  --launch-type FARGATE \
  --network-configuration 'awsvpcConfiguration={subnets=[subnet-12345],securityGroups=[sg-12345],assignPublicIp=ENABLED}'

Step 5: Check EFS Mount Issues

If task uses EFS volumes:

```bash # Check task definition for EFS configuration aws ecs describe-task-definition --task-definition my-task:1 \ --query 'taskDefinition.volumes[*].efsVolumeConfiguration'

# Verify EFS mount targets exist in task subnets aws efs describe-mount-targets --file-system-id fs-12345 ```

EFS requirements: - Mount targets in each subnet used by tasks - Security group allows NFS (port 2049) from task security group

Step 6: Check IAM Roles

1.Task needs two roles:
2.Task execution role - For pulling images, writing logs
3.Task role - For application to access AWS services

```bash # Check task execution role aws ecs describe-task-definition --task-definition my-task:1 \ --query 'taskDefinition.executionRoleArn'

# Verify role exists and has correct permissions aws iam get-role --role-name ecsTaskExecutionRole ```

Required trust policy:

json

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "Service": "ecs-tasks.amazonaws.com"
      },
      "Action": "sts:AssumeRole"
    }
  ]
}

Step 7: Check CloudWatch Logs

```bash # Get log configuration aws ecs describe-task-definition --task-definition my-task:1 \ --query 'taskDefinition.containerDefinitions[*].logConfiguration'

# Check if log group exists aws logs describe-log-groups --log-group-name-prefix /ecs/my-task ```

Create log group if missing:

bash

aws logs create-log-group --log-group-name /ecs/my-task

Step 8: Check Docker Events on Container Instance

For EC2 launch type, SSH into the instance:

```bash # Check Docker events docker events --filter 'type=container' &

# Check containerd logs journalctl -u containerd -f

# Check ECS agent logs tail -f /var/log/ecs/ecs-agent.log.* ```

Step 9: Review ECS Service Events

If task is part of a service:

bash

aws ecs describe-services --cluster my-cluster --services my-service \
  --query 'services[*].events[:5]'

Look for patterns like: - service my-service was unable to place a task - service my-service is unable to consistently start tasks

Step 10: Verify Port Mappings

Check for port conflicts:

```bash # Check task definition ports aws ecs describe-task-definition --task-definition my-task:1 \ --query 'taskDefinition.containerDefinitions[*].portMappings'

# Check what ports are in use on container instance aws ecs describe-container-instances \ --cluster my-cluster \ --container-instances arn:aws:ecs:region:account:container-instance/my-cluster/abc123 \ --query 'containerInstances[*].registeredResources[?name==PORTS]' ```

Verification

```bash # After fixing, restart task aws ecs run-task --cluster my-cluster --task-definition my-task:1

# Monitor task status aws ecs describe-tasks --cluster my-cluster --tasks NEW_TASK_ID \ --query 'tasks[*].[lastStatus,containers[*].lastStatus]' ```

Task should transition: - PENDING → RUNNING (within 1-2 minutes for EC2, 2-3 minutes for Fargate)

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Last updated: Apr 1, 2026

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Fix AWS ECS Task Stuck in Pending State

Introduction

Symptoms

Common Causes

Step-by-Step Fix

Step 1: Check Task Details and Stopped Reason

Step 2: Check Container Instance Resources

Step 3: Check Container Image Access

Step 4: Check Network Configuration

Step 5: Check EFS Mount Issues

Step 6: Check IAM Roles

Step 7: Check CloudWatch Logs

Step 8: Check Docker Events on Container Instance

Step 9: Review ECS Service Events

Step 10: Verify Port Mappings

Verification

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FixWikiHub Editorial Team

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Official Documentation & Further Reading

Fix AWS ECS Task Stuck in Pending State

Introduction

Symptoms

Common Causes

Step-by-Step Fix

Step 1: Check Task Details and Stopped Reason

Step 2: Check Container Instance Resources

Step 3: Check Container Image Access

Step 4: Check Network Configuration

Step 5: Check EFS Mount Issues

Step 6: Check IAM Roles

Step 7: Check CloudWatch Logs

Step 8: Check Docker Events on Container Instance

Step 9: Review ECS Service Events

Step 10: Verify Port Mappings

Verification

Related Issues

Related Articles

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