Security groups control the access that traffic has in and out of a DB instance. Three types of security groups are used with Amazon RDS: DB security groups, VPC security groups, and EC2 security groups. In simple terms, a DB security group controls access to a DB instance that is not in a VPC, a VPC security group controls access to a DB instance (or other AWS instances) inside a VPC, and an EC2 security group controls access to an EC2 instance.
By default, network access is turned off to a DB instance. You can specify rules in a security group that allows access from an IP address range, port, or EC2 security group. Once ingress rules are configured, the same rules apply to all DB instances that are associated with that security group. You can specify up to 20 rules in a security group.
Each DB security group rule enables a specific source to access a DB instance that is associated with that DB security group. The source can be a range of addresses (e.g., 203.0.113.0/24), or an EC2 security group. When you specify an EC2 security group as the source, you allow incoming traffic from all EC2 instances that use that EC2 security group. Note that DB security group rules apply to inbound traffic only; outbound traffic is not currently permitted for DB instances.
You do not need to specify a destination port number when you create DB security group rules; the port number defined for the DB instance is used as the destination port number for all rules defined for the DB security group. DB security groups can be created using the Amazon RDS APIs or the Amazon RDS page of the AWS Management Console.
For more information about working with DB security groups, see Working with DB Security Groups
Each VPC security group rule enables a specific source to access a DB instance in a VPC that is associated with that VPC security group. The source can be a range of addresses (e.g., 203.0.113.0/24), or another VPC security group. By specifying a VPC security group as the source, you allow incoming traffic from all instances (typically application servers) that use the source VPC security group. VPC security groups can have rules that govern both inbound and outbound traffic, though the outbound traffic rules do not apply to DB instances. Note that you must use the Amazon EC2 API or the Security Group option on the VPC Console to create VPC security groups.
DB instances deployed within a VPC can be configured to be accessible from the Internet or from EC2 instances outside the VPC. If a VPC security group specifies a port access such as TCP port 22, you would not be able to access the DB instance because the firewall for the DB instance provides access only via the IP addresses specified by the DB security groups the instance is a member of and the port defined when the DB instance was created.
You should use TCP as the protocol for any VPC security group created to control access to a DB instance. The port number for the VPC security group should be the same port number as that used to create the DB instance.
The following table shows the key differences between DB security groups and VPC security groups.
|DB Security Group||VPC Security Group|
|Controls access to DB instances outside a VPC||Controls access to DB instances in VPC.|
|Uses Amazon RDS APIs or Amazon RDS page of the AWS Management Console to create and manage group/rules||Uses Amazon EC2 APIs or Amazon VPC page of the AWS Management Console to create and manage group/rules.|
|When you add a rule to a group, you do not need to specify port number or protocol.||When you add a rule to a group, you should specify the protocol as TCP, and specify the same port number that you used to create the DB instances (or Options) you plan to add as members to the group.|
|Groups allow access from EC2 security groups in your AWS account or other accounts.||Groups allow access from other VPC security groups in your VPC only.|
A common use of an RDS instance in a VPC is to share data with an application server running in an EC2 instance in the same VPC and that is accessed by a client application outside the VPC. For this scenario, you would do the following to create the necessary instances and security groups. You can use the RDS and VPC pages on the AWS Console or the RDS and EC2 APIs.
Create a VPC security group (for example, "sg-appsrv1") and define inbound rules that use as source the IP addresses of the client application. This security group allows your client application to connect to EC2 instances in a VPC that uses this security group.
Create an EC2 instance for the application and add the EC2 instance to the VPC security group ("sg-appsrv1") you created in the previous step. The EC2 instance in the VPC shares the VPC security group with the DB instance.
Create a second VPC security group (for example, "sg-dbsrv1") and create a new rule by specifying the VPC security group you created in step 1 ("sg-appsrv1") as the source.
Create a new DB instance and add the DB instance to the VPC security group ("sg-dbsrv1") you created in the previous step. When you create the instance, use the same port number as the one specified for the VPC security group ("sg-dbsrv1") rule you created in step 3.
The following diagram shows this scenario.
For more information on working with DB security groups, go to Working with DB Security Groups.