subject: What is a security group in AWS? [print this page]
A security group in Amazon Web Services (AWS) acts as a virtual firewall for your EC2 instances (and some other AWS resources like RDS databases, ElastiCache clusters, etc.). It controls the inbound and outbound traffic at the instance level. Think of it as a set of rules that dictate what network traffic is allowed to reach your instance and what traffic your instance is allowed to send out. AWS Training in Pune
Here are the key aspects of security groups:
Instance-Level Firewall: Security groups are associated with network interfaces attached to your instances. Each instance can have multiple security groups associated with it, and the rules are aggregated to determine allowed traffic. Stateful: Security groups are stateful. This means that if you allow inbound traffic on a specific port and protocol, the corresponding outbound response traffic is automatically allowed, regardless of the outbound rules. You don't need to explicitly create an outbound rule to allow responses to established inbound connections. Allow Rules Only: Security groups only support allow rules. There are no "deny" rules. If no rule explicitly allows traffic, it is implicitly denied. Default Deny: By default, a newly created security group denies all inbound traffic and allows all outbound traffic. You need to explicitly add rules to allow specific inbound traffic. Rule Specification: When you define a security group rule, you specify: Protocol: The network protocol (e.g., TCP, UDP, ICMP, All). Port Range: The range of ports for the specified protocol (e.g., 80 for HTTP, 22 for SSH, 1-65535 for all ports). For ICMP, you specify the type and code. Source (for Inbound Rules): The source of the traffic. This can be: A specific IP address or CIDR block (e.g., 192.0.2.0/24, 203.0.113.5/32). Another security group within the same VPC. This allows instances within that source security group to communicate with the instances in the current security group. A prefix list (a managed list of CIDR blocks). "Anywhere" (0.0.0.0/0 for IPv4 or ::/0 for IPv6), which should be used cautiously as it allows traffic from all internet IPs. Destination (for Outbound Rules): The destination of the traffic. This can be: A specific IP address or CIDR block. Another security group within the same VPC. A prefix list. "Anywhere" (0.0.0.0/0 for IPv4 or ::/0 for IPv6). Description (Optional but Recommended): A description to help you understand the purpose of the rule. Dynamic Updates: Changes to security group rules are applied immediately to all associated instances without requiring a restart. VPC Specific: Security groups are specific to a Virtual Private Cloud (VPC). You cannot directly use a security group created in one VPC with resources in another VPC (unless VPC peering or Transit Gateway is configured). In essence, security groups provide a fundamental layer of network security for your AWS resources, allowing you to control precisely who and what can communicate with your instances. They are a crucial component of the AWS shared responsibility model, where AWS secures the infrastructure, and you are responsible for securing what you build on top of it, including configuring your security groups appropriately.
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