What is the shared responsibility model in cloud security?

The shared responsibility model in cloud security defines how security tasks are divided between a cloud provider and its customers. In simple terms, the provider secures the underlying infrastructure (like data centers, hardware, and hypervisors), while the customer is responsible for securing what they deploy in the cloud, such as applications, data, and access controls. This division varies slightly depending on the service model (IaaS, PaaS, SaaS), but the core idea remains: security is a joint effort, not one party’s job. For example, AWS, Azure, and Google Cloud all follow this model, but the exact responsibilities shift based on the services you use.

Let’s break this down with concrete examples. In an Infrastructure-as-a-Service (IaaS) setup, the cloud provider manages physical security, network infrastructure, and virtualization layers. The customer, however, must secure the operating system, applications, and data stored on virtual machines. If a developer deploys a VM on AWS EC2, AWS ensures the server hardware is protected, but the developer must patch the OS, configure firewalls, and encrypt sensitive data. For Platform-as-a-Service (PaaS) offerings like Azure App Service, the provider takes over more layers (runtime, middleware), leaving the customer to focus on application code and data security. A common mistake here is assuming the provider handles everything—for instance, if a database in Google Cloud SQL is left publicly accessible due to misconfigured access rules, that’s the customer’s responsibility, not Google’s.

Developers play a critical role in upholding their side of the model. Cloud providers offer tools like IAM policies, encryption services, and network security groups, but it’s up to developers to use them effectively. For example, enabling multi-factor authentication for user accounts, encrypting data at rest using AWS KMS, or setting up VPCs to isolate resources are all customer responsibilities. Ignoring these can lead to breaches, like the infamous S3 bucket leaks caused by misconfigured permissions. The model only works when both parties do their part: providers secure the foundation, and developers secure what they build on top of it. Understanding this split is key to avoiding gaps and ensuring end-to-end security.