KAUSTUBH SHARMA
learn

AWS EC2 Cannot Connect — Troubleshooting Guide

Diagnose common EC2 connectivity failures by separating network, identity, host, and service-layer causes.

1 min readLevel: IntermediateUpdated Current
Learning progression1 min read
BeginnerIntermediateAdvancedProduction
troubleshootingAWSEC2networkingsecurity

Troubleshooting

Start with the symptom. End with a verified fix.

What’s wrong?

An EC2 instance cannot be reached through SSH, RDP, or an application endpoint.

Possible causes

  1. Security group or network ACL rules
  2. route or subnet configuration
  3. host-level firewall or service failure
  4. wrong address or port
  5. instance health problem

Diagnosis

  1. Confirm the target address and port
  2. check instance and system health
  3. inspect security groups and network ACLs
  4. validate subnet routes and connectivity
  5. test the host service locally

2 · Fix

Correct the smallest confirmed network or host configuration issue and avoid broad allow rules.

Verify

Reconnect from the expected client and verify the application endpoint, logs, and telemetry.

3 · Prevent

Keep least-privilege network rules, health monitoring, and a documented connectivity runbook.

AWS EC2 Cannot Connect

When an EC2 instance is unreachable, separate the problem into address → network path → security controls → host → service.

Diagnose

  1. Confirm the expected hostname/IP, port, and protocol.
  2. Check EC2 instance and system status checks.
  3. Verify the subnet route table and expected internet, NAT, VPN, or private connectivity path.
  4. Inspect security groups and network ACLs.
  5. Check the operating-system firewall and target service.
  6. Compare a working instance in the same path.

Fix → Verify → Prevent

Fix only the layer supported by evidence. After the change, reconnect and confirm the application itself responds. Prevent recurrence with least-privilege rules, health checks, and a short connectivity runbook.

Related: architecture, cloud concepts.

Engineering companion

Learn → troubleshoot → design → prepare → test

Explore the knowledge graph →
LearnAWS SERVICES IN ONE WORDTroubleshootAmazon S3 AccessDenied — Troubleshooting GuideDesignArchitecture Decision GuideInterviewReal-World Cloud Interview QuestionsQuizAWS Certified Generative AI Developer - Professional (AIP-C01)

Knowledge path

Connected concepts

Explore the knowledge graph →
troubleshootingAWSEC2networkingsecurity

Explore next

K8s ArchitectureLinked knowledge →Elasticity vs Scalability vs Agility vs High Availability vs Fault Tolerance vs Disaster RecoveryConnected concept →