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Create Security Group Rules | Terraform Module

You avoid hundreds of lines of similar security group definitions by using this rule creation module.

In just one line with words like ssh, https, sftp, rabbitmq, openvpn or all-traffic you specify every AWS security group rule that you need. This module always creates a new security group because Terraform cannot correctly adopt the VPC's default security group - it exhibits problems setting the descriptions and fails as it attempts to destroy it.

Usage

module security_group {

    source  = "devops4me/security-group/aws"
    version = "~> 1.0.0"

    in_ingress = [ "ssh", "http", "https" ]
    in_vpc_id  = module.vpc.out_vpc_id
}

resource aws_instance ec2
{
    vpc_security_group_ids = [ module.security_group.out_security_group_id ]
}

out_security_group_id is the fundamental module output string variable.

Run the Example

You can run the example to see this module create a number of VPCs with varying attributes such as the number of private/public subnets.

Use Case

What is the use case flow at the heart of this security group rule creation module?

  • a VPC is mandatorily provided
  • a new security group is created
  • ingress and egress rules are added to the security group
  • the default source (and/or destination) of 0.0.0.0/0 is used
  • the rules can apply the specified IP address ranges (through CIDR blocks for the source and/or destination of traffic to allow.

Module Inputs

The security group's input variables are vital to achieving the desired behaviour.

Imported Type Default Comment
in_vpc_id string vpc-1234567890 create security group/s under VPC with this id
in_ingress list [ "postgres", "https"] identify the ports to allow for inbound traffic
in_egress list [ "all-traffic" ] identify the ports to allow for outbound traffic
in_ingress_cidr_blocks list [ "0.0.0.0/0"] list of source incoming traffic addresses to allow
in_egress_cidr_blocks list [ "0.0.0.0/0"] list of VPC source outgoing traffic addresses to allow
in_ecosystem string kube-19188-2306 the ecosystem's identifier including a timestamp

Alternate Module Inputs

This security group module is simple but flexible as it needs to cater to many different tastes. Now follows a number of overloading facilities to craft your security group's behaviour.

Specify the Creation of a Security Group

This security-group module adds ingress and egress rules to either the default or a new security group within a given VPC.

Passing false to the in_use_default flag causes the creation of a security group.

module security_group_module {

    source  = "devops4me/security-group/aws"
    version = "~> 1.0.0"

    in_vpc_id  = module.xyz.out_vpc_id
    in_ingress = [ "ssh", "http", "https" ]
    in_egress  = [ "all-traffic" ]
}

Note that this module only creates one security group at a time. To create two or more simply repeat the module declaration using a different name each time.

Specify Ingress and Egress Cidr Blocks

Most security group source cidr blocks allow traffic originating from anywhere ( 0.0.0.0/0 ).

This is true for both inress (incoming) and egress (outgoing) traffic. You can alter this by specifying these extra module inputs. The below allows traffic in only from a given VPC and out only from a subnet within the security group's VPC.

in_ingress_cidr_blocks = [ "172.30.0.0/16" ]
in_egress_cidr_blocks  = [ "10.2.0.4/24" ]

The cidr blocks are lists of strings so you can also allow traffic from more than one source block.

in_ingress_cidr_blocks = [ "172.30.0.0/0", "82.9.72.144/31" ]

Specify Other Ingress and Egress Rules

Clearly you will want to allow ingress and egress traffic for various middleware services.

@todo Author then link to sister page containing a table full of rule classifications.

Note that if you create an all traffic egress rule and you have an IPV6 cidr block, AWS will create an extra ::/0 egress rule in addition to the 0.0.0.0/0 (IPV4) rule.

Optional Resource Tag Inputs

Most organisations have a mandatory set of tags that must be placed on AWS resources for cost and billing reports. Typically they denote owners and specify whether environments are prod or non-prod.

Input Variable Variable Description Input Example
in_ecosystem the ecosystem (environment) name these resources belong to my-app-test or kubernetes-cluster
in_timestamp the timestamp in resource names helps you identify which environment instance resources belong to 1911021435 as $(date +%y%m%d%H%M%S)
in_description a human readable description usually stating who is creating the resource and when and where "was created by $USER@$HOSTNAME on $(date)."

Try echo $(date +%y%m%d%H%M%S) to check your timestamp and echo "was created by $USER@$HOSTNAME on $(date)." to check your description. Here is how you can send these values to terraform.

export TF_VAR_in_timestamp=$(date +%y%m%d%H%M%S)
export TF_VAR_in_description="was created by $USER@$HOSTNAME on $(date)."

Module Outputs

Exported Type Comment
out_security_group_id String ID of the security group that contains the specified rules