Rules Engine for Firewall

Implement security logic, based on criteria and behaviors, with Rules Engine for Firewall.

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The Rules Engine for Firewall is a feature designed to implement security logic for your applications. You can find the Rules Engine settings tab within a created firewall.

The Rules Engine is programmable, allowing you to define the conditions (Criteria) and actions (Behaviors). If the Criteria are met, the Behaviors will be executed.

You can use the Rules Engine for Firewall to configure all operational aspects of your application’s firewalls. Here are some implementations examples you can use it for:

  • Blocking a request.
  • Ignoring a request.
  • Limiting the access rate.
  • Applying a Web Application Firewall (WAF) policy.
  • Running an Function for Firewall with your own security code.
  • Monitoring traffic to identify threats.

A firewall can have as many rules as needed. These rules are interchangeable, allowing you to share the same rule across all other firewalls.

Go to Firewall Reference Go to Work With Rules Engine Guide

Implementation

ScopeResource
Secure an applicationHow to secure an application
Configuring main settingsHow to configure Firewall main settings
Creating a WAF rule setHow to create a WAF rule set
Blocking Tor exit node IP addressesHow to block Tor exit node IP addresses

How Rules Engine for Firewall works

Each request from your users to your application is processed first by Firewall. You can define a set of security rules within Firewall.

The rules are composed by Criteria, which represent the conditions for executing the rules, and by Behaviors, which represent the actions to be executed.

The processing of the rules is sequential and you can use them as a powerful set of variables and comparison operators. If the conditions are met, the Behaviors of each rule are executed until all the rules are processed.

A firewall is composed of several key components that define its functionality and operation. While configuring a firewall, you can define its main settings, including: a Name, the Domains that will be secured by the firewall, and the Modules that will be used to extend the usability of Rules Engine, as well as enable the Debug Rules feature.

After that, you’ll be able to add Functions Instances and Rules Engine rules. The fields and requirements to use Rules Engine for Firewall are explained in the sections below.

Name

Each rule must have a unique and easy-to-remember name, allowing you to easily reference and manage it within your system.

Description

Aside from the name of the rule, you can add a description to your rule using the Description field. Your description will be visible from the rule list and can be used to help you identify what the rule does.

Criteria

The Criteria section of Rules Engine for Firewall is where you define the conditions for executing the rule. Criteria are composed of:

  • Variables
  • Comparison operators
  • Logic operators
  • Arguments, when applicable

The inclusion of arguments in a criteria depends on the comparison operators chosen. The format of the arguments is described in the variables and comparison operators sections below. You can also add logical operators to increase the amount of comparisons that the rule will execute.

For example, this criteria identifies requests where the URI starts with a forward slash (”/”) so that the defined behavior can then be applied to them.

VariableComparison operatorArgument
IfRequest URIstarts with/

The availability of certain criteria depends on the enabled modules of your Firewall. Go to the Firewall modules reference for more details.

Variables

These are all the Criteria variables you can set:

VariableDescriptionExampleRequirements
Header AcceptHeader that tells you what types of media the customer accepts for the response.application/jsonWeb Application Firewall
Header Accept EncodingHeader that tells you what types of content encoding, usually compression algorithms, that the client accepts for the responsegzipWeb Application Firewall
Header Accept LanguageHeader that informs the expected languageen-USWeb Application Firewall
Header CookieHeader containing the cookies sent by the client in the request to the serversession_id=abc123Web Application Firewall
Header OriginHeader that informs the origin of a cross-site access request or a preflight request. The source is a URI indicating the name of the server, with no path informationhttps://example.comWeb Application Firewall
Header RefererHeader indicating the address of the document, or element in a document, from which the request’s URI was obtainedhttps://example.com/landing-pageWeb Application Firewall
Header User AgentHeader with a characteristic string that allows servers to identify the application, operating system, vendor, and/or version of the deviceMozilla/5.0Web Application Firewall
Request ArgsAll arguments sent by the user in the request string (query string).page=1Web Application Firewall
NetworkThe IP address of the client making the HTTP request, which can be used for any network comparison (CIDR, ASN or Country)1xx.xxx.x.0Network Shield
HostIn order of precedence: the hostname of the request line, or the value of the Host header field of the request, or the name of the server serving the requestapi.example.com-
Request MethodThe request’s HTTP method. For example: GET, POST, PUT, etc.POST-
Request URIThis relates to the ${uri} variable from Rules Engine for Applications. The normalized (urldecoded) URI of the request. The value of ${uri} can change during the processing of a request, for example, when an internal redirect occurs or when index files are used. It doesn’t carry the Query String parameters as ${request_uri} do./api/v1/-
SchemeThe scheme of the request: HHTP or HTTPS.https-
Client Certificate ValidationServer process to authenticate client digital certificate.true-
SSL Verification StatusServer result to client certificate validation. It can be Success, when the client certificate validation passed; Certificate Verification Error, when the client certificate wasn’t valid; and Missing Client Certificate, when the client certificate wasn’t sent in the request.Certificate Verification Error-

Comparison operators

The condition for the execution of a rule must be the comparison of a variable with an argument. The comparison operators are:

OperatorDescriptionArgument type
is equalThe value of the variable is equal to the argument, compared character by characterString
is not equalThe value of the variable isn’t exactly the same as the argumentString
starts withThe value of the variable starts with the argumentString
does not start withThe value of the variable doesn’t start with the argumentString
matchesThe value of the variable matches the regular expression or list entered as an argumentRegular expression or list
does not matchThe value of the variable doesn’t match the regular expression entered as an argumentRegular expression or list
existsThe variable has a defined value. For example, Request Args exists if an argument is sent in the request’s query string-
does not existThe variable doesn’t have a defined value. For example, Request Args doesn’t exist if an argument is sent in the request’s query string-

These operators may vary according to the selected Criteria.

Logic operators

Multiple criteria can be defined using the logical operators And and Or.

The operator And has implicit precedence over the operator Or.

If explicit precedence is required, you can add multiple criteria groups under the And logic.

Behaviors

In the Behaviors section of the Rules Engine, you must add the behaviors you want your rule to perform if the conditions defined in the criteria are met.

For example, this behavior runs the specified function, allowing you to execute custom logic for handling requests.

BehaviorArgument
Run Function<name-of-the-instantiated-function>

Deny (403 Forbidden)

It closes the request with an HTTP 403 Forbidden response. No arguments are required.

Drop (Close Without Response)

It closes the request without responding to the customer. No arguments are required.

Set Rate Limit

It defines an access rate limit that, if exceeded, will result in an HTTP 429 Too Many Requests response. To configure the Rate Limit, you must inform:

  • Type is the field to select the type of request for the Rate Limit, choosing Req/s (requests per second) or Req/min (requests per minute).
  • Average Rate Limit, which is the limit rate itself by second.
  • Client IP address, if you want the access rate to be counted by the client’s IP address or Global, if you want total access rate counted.
  • Maximum burst size, which indicates the maximum burst size of HTTP requests sent simultaneously, which will be queued and dispatched gradually, respecting the limit rate.
    • The configured value will be the Rate Limit for each Azion Edge Node, implemented using the Leaky Bucket algorithm. It’s recommended to use Maximum burst size at a maximum of 10 times of the value configured in Average Rate Limit, which would result in penalizing the last request for a burst with up to a 10 second delay.

As the Rate Limit is applied by IP address of Global and by rule, if a rule has more than one URI specified and uses the conditional Or, the rate limit will be shared between the URIs. Create different rules if you wish to have a Rate Limite for each URI.

The Maximum Burst size is only available for the Req/s (request per second).

Set WAF Rule Set

Requires WAF

It associates the WAF Rule Set to be used in the request. WAF policies must be previously configured in Edge Libraries > WAF Rules. You must also define the WAF mode: Learning or Blocking. Read more on WAF Rule Sets.

Run Function

Requires Functions

It runs a function specified as a parameter. The function must have been previously instantiated and parameterized in the Functions tab in order to be used.

Set Custom Response

It allows a customized response when the request matches the criteria. You can customize the Status Code by changing it from 200 to 499, the Content Type header, and Content Body of your request with a maximum of 500 characters.

Behaviors execution and logic

While behaviors and rules are executed in the order they’re arranged, some behaviors can’t be stacked.

If a behavior of the type Set, such as Set Custom Response in Firewall and Set Origin in Applications, is added multiple times to the rules in Rules Engine, only the last behavior from the last rule in which the criteria was met will be executed.

Behaviors of the type Add are cumulative and can be added multiple times to rules. This means that if Add Cookie and Add Header are executed multiple times for the same key-value pairs, multiple identical entries will be added.

However, for unique headers such as Host, the last behavior of type Add Header that is executed will overwrite the previous value, since there can’t be more than one Host header in a request.

Some behaviors, such as Deny, can finish the execution of rules. If a sequence of rules includes such behavior, any rules or behaviors that follow this type of finalizing behavior won’t be executed.

Debugging rules

You can debug rules created with Rules Engine for Firewall through the GraphQL API, Data Stream, or Real-Time Events.

Watch a video tutorial about programming Firewall rules for optimal WAF usage and cost optimization on Azion’s YouTube channel: