How can I troubleshoot and resolve the issue of “AWS 502 bad gateway”?

In the context of AWS, here are the steps given of how you can troubleshoot and resolve this particular issue:-

Initial command

You can use the “curl” or “wget” command so that you can directly access the URL that is causing the issue.

Logs examination

You can access AWS cloud watch logs for your elastic Beanstalk environment. You should look for the logs that are related to the load balancer, application, and server Instance.

Configuration check

You can review your elastic beanstalk environment’s load balancer setting for listeners Configuration.

Load balancer insights

You can use the AWS CLI or AWS management console to analyse elastic load balancer metrics.

Health checks and scaling

You can also adjust the elastic Beanstalk health Checking setting to ensure the Instance passes the health check before receiving the traffic.

Here is the example given of the steps:-

# Step 1: Initial Assessment

# Use curl to check the HTTP response code

Curl -I https://your-website.com

# Step 2: Logs Examination

# Use AWS CLI to retrieve Elastic Beanstalk logs

Eb logs

# Use AWS CLI to access CloudWatch Logs Insights

Aws logs start-query –log-group-name /aws/elasticbeanstalk/YourEnvironmentName/var/log/httpd/access_log

# Step 3: Configuration Check (Adjusting Load Balancer Idle Timeout)

# Create or modify AWS CloudFormation template (e.g., load_balancer.yaml)

Resources:

  MyLoadBalancer:

    Type: AWS::ElasticLoadBalancingV2::LoadBalancer

    Properties:

      LoadBalancerAttributes:

Key: idle_timeout.timeout_seconds

          Value: “60”

# Step 4: Load Balancer Insights (Get Load Balancer Metrics)

# Use AWS CLI to get metrics from the load balancer

Aws cloudwatch get-metric-data –metric-data-queries MetricName=HTTPCode_Target_5XX_Count,Period=300,Stat=Sum,Unit=Count –start-time $(date -d ‘5 minutes ago’ +%s) –end-time $(date +%s) –namespace AWS/ApplicationELB –dimensions Name=LoadBalancer,Value=YourLoadBalancerName –region YourRegion

# Step 5: Health Checks and Scaling (Modify Elastic Beanstalk Health Check Settings)

# Create or modify Elastic Beanstalk configuration file (e.g., health_check.config)

Resources:

  AWSEBAutoScalingGroup:

    Type: AWS::AutoScaling::AutoScalingGroup

    Properties:

      HealthCheckType: ELB

      HealthCheckGracePeriod: 300

# Step 6: Application Code Analysis (Example Python Flask Code)

# Example Python Flask application code

From flask import Flask, jsonify

App = Flask(__name__)

@app.route(‘/’)

Def index():

    # Simulate a 502 Bad Gateway error

    Return jsonify({‘error’: ‘502 Bad Gateway’}), 502

If __name__ == ‘__main__’:

    App.run(debug=True)

# Step 7: Testing and Monitoring (Create CloudWatch Alarm)

# Create CloudFormation template for CloudWatch Alarm (e.g., cloudwatch_alarm.yaml)

Resources:

  Http5xxAlarm:

    Type: AWS::CloudWatch::Alarm

    Properties:

      AlarmDescription: “HTTP 5xx Errors Alarm”

      Namespace: “AWS/ApplicationELB”

      MetricName: “HTTPCode_Target_5XX_Count”

      Dimensions:

Name: LoadBalancer

          Value: YourLoadBalancerName

      Statistic: “Sum”

      Period: 300

      EvaluationPeriods: 1

      Threshold: 1

      ComparisonOperator: “GreaterThanOrEqualToThreshold”

      AlarmActions:

YourSnsTopicArn