Shared Responsibility Model

Learn which security and operational responsibilities belong to AWS and which belong to the customer.

Last reviewed: June 2026

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Quick Understanding: Shared Responsibility Model helps teams design, build, secure, operate, and troubleshoot AWS workloads. In enterprise projects, the important questions are ownership, blast radius, automation, observability, compliance, and cost.

🔍 What Is It?

The AWS Shared Responsibility Model explains who is responsible for what.

AWS is responsible for security of the cloud: data centers, physical hardware, managed infrastructure, and foundational services.

Customers are responsible for security in the cloud: identity, data, network access, application code, configurations, encryption choices, backups, and monitoring.

🎯 Why Do We Need It?

Many AWS incidents happen because teams assume AWS manages more than it does.

The model helps architects assign accountability for patching, access control, encryption, logging, backups, compliance evidence, and incident response.

Common developer mistakes:

  • →Choosing defaults without checking security, cost, or failure behavior
  • →Treating AWS services as isolated tools instead of part of an architecture
  • →Skipping tags, alarms, IAM review, backups, and runbooks until production incidents happen
  • →Building manually in the console and then struggling to reproduce environments

🏗️ What Happens in Real Projects?

For EC2, AWS secures the physical host and hypervisor, while the customer patches the guest OS, configures security groups, manages IAM, and protects application data.

For managed services such as S3 or RDS, AWS handles more infrastructure work, but the customer still owns access policies, encryption choices, data classification, retention, and monitoring.

⚙️ How It Works

Responsibility shifts depending on service type.

Infrastructure services give the customer more control and more responsibility. Managed services reduce operational burden but still require secure configuration. Serverless services move more infrastructure management to AWS, but code, identity, data, and event permissions remain customer concerns.

💻 Example

Responsibility comparison — How responsibility changes by service model.

text
EC2:
  AWS owns: facilities, hardware, hypervisor
  Customer owns: OS patching, app code, firewall rules, data

RDS:
  AWS owns: database host infrastructure and managed patch options
  Customer owns: schema, users, access, backups policy, data protection

Lambda:
  AWS owns: runtime infrastructure
  Customer owns: function code, IAM permissions, secrets, event sources

🤔 Common Confusions

❓ Does AWS patch my EC2 operating system?

No. Customers manage guest OS patching unless they use specific managed services or automation they configure.

❓ Does using S3 mean my bucket is automatically secure?

No. Customers own bucket policies, public access settings, encryption configuration, and data governance.

❓ Is compliance fully handled by AWS?

No. AWS provides compliant infrastructure and reports, but customers must configure workloads and maintain evidence correctly.

🚨 Common Production Issues

**Unpatched EC2 instances** because teams assume AWS handles guest OS maintenance.

**Public data exposure** from incorrect S3 or IAM policies.

**No audit evidence** for customer-owned controls.

**Misconfigured encryption** where keys, rotation, or access are not governed.

✅ Best Practices

Map responsibilities for each service in architecture reviews

Use managed services to reduce undifferentiated operations where suitable

Automate customer-owned controls such as patching, backup, and IAM review

Collect CloudTrail, Config, and security findings for evidence

Document ownership in runbooks and onboarding material

🏛️ Architect's Note

Senior Architect's Perspective

The shared model is an accountability tool. Mature AWS teams do not say "AWS handles security"; they say exactly which controls AWS handles and exactly which controls the team must prove.

💬 Frequently Asked Questions

Interview: How would you explain Shared Responsibility Model in a real AWS project?

Shared Responsibility Model should be explained through the business workload it supports, the AWS responsibility boundary, the failure modes, the security controls, and how it is monitored and automated.

Interview: What production mistake do developers commonly make with Shared Responsibility Model?

The common mistake is using the service successfully in a lab but not designing for least privilege, multi-AZ resilience, alarms, cost visibility, and repeatable infrastructure.

How does the model affect interviews?

Interviewers often ask whether you know which tasks move to AWS and which remain customer responsibilities. Use EC2 versus RDS versus Lambda examples.

Who owns application vulnerabilities?

The customer owns application code, dependencies, configuration, and secure deployment practices.

🎯 Key Takeaways

1AWS secures the cloud infrastructure
2Customers secure their workloads, identities, data, and configurations
3Responsibility changes by service model
4Managed services reduce but do not eliminate customer responsibility

🎯 Practice this topic in interviews

↗ Where this topic fits

Sources

Sources / References

Use these AWS references to verify the concept in official docs and continue into the most relevant SplashRide pages.