Standard UNIX tools for manipulating AWS security group rules

## Concepts

Security Groups rules in AWS have four basic components. In Situ and this documentation, we refer to them as follows:

• A direction, “in” (ingress) or “out” (egress)

• An owner, the group to whom the rule belongs

• An other, the subject of the rule, which may be a security group or CIDR

• A portspec, consisting of an IP protocol, low port, and high port

## Included Tools

Situ includes two tools for managing security group rules: sgtables and sgmanager.

sgmanager is a higher-level tool used for managing more human-friendly rule representations. sgmanager depends on sgtables to make changes in AWS.

stgables is a low-level (raw) rule processor. It consumes and generates basic rule definitions, and is capable of modifying rulesets in AWS.

These tools only manage security group rules. They do not create or remove the groups themselves.

## Using sgmanager

There are currently three sgmanager subcommands:

• groupdefs, a tool for extracting group definitions in the sgmanager

• format render, which accepts one or more configuration files and renders them to raw rules suitable for consumption by sgtables

• reverse, which can help you convert sgtables output to a set of rules

When using sgmanager, vars_files are files in the sgmanager configuration format as outlined below. input_files refer to files containing raw rules as output by sgtables.

### sgmanager Configuration

There are four entity types that can be defined in an sgmanager configuration:

• Rule - represents a single IpPermission on a SecurityGroup

• SecurityGroup - represents a single AWS SecurityGroup

• Cidr - An IPv4 CIDR address/mask

• Account - an AWS account

The syntax of an sgmanager configuration is:

<rule>          ::= "rule " <Direction> " " <SecurityGroup:NAME> " " ( <SecurityGroup:NAME> | <Cidr:NAME> ) " " <PortSpec:NAME>

<SecurityGroup> ::= "sg " NAME " " SG_ID

<Cidr>          ::= "cidr " NAME " " IPADDR "/" INT_MASK

<Account>       ::= "acct " NAME " " ACCOUNT_ID

<PortSpec>      ::= "proto " NAME " " <Protocol> " " <Lport> " " <Hport>
<Protocol>      ::= ( "icmp" | "tcp" | "udp" | -1 | 0 | POSITIVE_INTEGER )
<Lport>         ::= -1 | 0 | POSITIVE_INTEGER
<Hport>         ::= -1 | 0 | POSITIVE_INTEGER

Where:

• SG_ID is an AWS security group id

• INT_MASK is an integer between 0 and 32 (inclusive)

• ACCOUNT_ID is an AWS numeric account ID

For port numbers, POSITIVE_INTEGER can be between 1 and 65535, and -1 means all.

### Example

Suppose you have a sgmanager configuration file named “myrules” containing the following:

acct prd 11223344556677

cidr prd-w1 10.208.0.0/16

sg prd-w1-eop sg-12345678
sg prd-w1-app sg-abcdef12

proto ssh tcp 22 22

rule in prd-w1-eop prd-w1-app ssh
rule in prd-w1-eop prd-w1 ssh

Running sgmanager prd myrules would produce the following output:

in sg-12345678 sg-abcdef12 tcp 22 22
in sg-12345678 10.208.0.0/16 tcp 22 22

## Using sgtables

sgtables has four functions: list, add, remove, and update

sgtables always requires an AWS profile (from ~/.aws/config), a region, and a specific VPC to operate against (or the special name ‘classic’ for EC2 Classic). sgtables only operates on one network at a time. EC2 classic is handled as its own network/VPC.

All data-modification commands (everything except list) accept a --noop argument (for no-op) that prevents any real changes from taking place. You can use the --verbose flag to see more detail about the operations performed by the command. --debug will also include low-level details.

The add command will try to add all rules passed to it (so long as the group exists in the VPC). Similarly, remove will try to remove all rules passed to it. You will be warned if the given rule already exists (for add) or if it is not found (for remove), but this will not cause sgtables to fail.

update behaves somewhat differently than the other two. Before making changes, update inspects the current ruleset and compares it to the input given. For any security group mentioned as an owner in the rules list, rules are added if needed, then rules are removed. To put it another way, update expects that the rules passed to it are the only rules that should be in those groups.

Mentioned, in this context, means that any rule not listed as an owner in the ruleset will not be updated. sgtables can update all rules in all security groups in a VPC if passed the ominuously-named --obliterate flag to update. When --obliterate is specified, sgtables assumes that the rules given to it are the only rules that should exist in the VPC. If a group exists but no rules are defined for it, that group will have all of its rules removed.

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