If the response time of your website is increased due to HTTP flood attacks, you can enable the rate limiting feature and use default or custom rules to block specific requests that are sent to your website. This feature blocks requests within seconds and improves website security. This topic describes how to configure rate limiting.

Step 1: Apply for the rate limiting feature

You must apply for the rate limiting feature before you can use this feature. To apply for this feature, you can join one of the following DingTalk groups:
  • Group 1: 23184221. No more members can be added to the group.
  • Group 2: 33298914. No more members can be added to the group.
  • Group 3: 33137775.

Step 2: Enable the rate limiting feature

  1. Log on to the Alibaba Cloud CDN console.
  2. In the left-side navigation pane, click Domain Names.
  3. On the Domain Names page, find the domain name that you want to manage and click Manage in the Actions column of the domain name.
  4. In the left-side management pane of the domain name, click Security Settings.
  5. Click the Rate Limiting tab.
  6. Turn on Rate Limiting.
  7. Click Modify.
  8. In the Rate Limiting dialog box, enable Parameter Check and set Control Mode.
    Configure rate limiting
    Parameter Description
    Parameter Check After the parameter check feature is enabled, the rate limiting feature compares the specified URIs with all parameters retained with requests. The parameter check feature checks only URIs. Custom match rules that are set for the custom rate limiting mode do not apply to the parameter check feature.
    Note Parameter check takes effect only in custom rate limiting rules.
    Control Mode You can select one of the following modes:
    • Normal

      The default rate limiting mode. Select this mode to prevent false positives if the network traffic of your website is within the expected range.

    • Emergency

      Select this mode if your website responds slowly and exceptions are detected in network traffic, CPU usage, memory usage, and other performance indicators.

    • Custom

      Select this mode if you want to customize rate limiting rules based on your business requirements. This mode detects requests that access your website more frequently than expected, and mitigates HTTP flood attacks on CDN edge nodes. For more information about how to create a custom rate limiting rule, see Step 9.

  9. Optional:Create a custom rule
    Note
    • When you set Control Mode to Custom, you must create a custom rate limiting rule. Other control modes do not require custom rate limiting rules.
    • You can create a maximum of five custom rate limiting rules.
    1. Click Add Rule on the right side of Custom Rules.
    2. Follow the instructions to create a custom rule. The following table describes the parameters.
      Parameters used to create a custom rule
      Parameter Description
      Rule Name
      • The name must be 4 to 30 characters in length, and can contain letters and digits.
      • The names of rules that are set for the same accelerated domain name must be unique.
      URI Enter the URI that you want to protect, for example, /register. You can include parameters in the URI, for example, /user?action=login. You must also enable the parameter check feature if you want to apply the rule to the entire URI.
      Matching mode You can select one of the following match rules. The rate limiting rule applies the match rules in the following order: exact match, prefix match, and fuzzy match. You can adjust the priorities of the match rules in a rate limiting rule. The match rules are listed and executed based on their priorities.
      • Exact Match

        In this mode, requests are counted only if the request URI exactly matches the specified URI.

      • Prefix Match

        In this mode, requests are counted if the request URI starts with the specified URI. For example, if the URI is set to /register, requests that are sent to /register.html are counted.

      • Fuzzy Match
        In this mode, requests are counted if the request URI matches the specified regular expression. Regular expressions support only periods (.)and asterisks (*).
        • A period (.) specifies that the rate limiting rule compares each individual character.
        • An asterisk (*) specifies that the rate limiting rule considers the request a match if any character matches the specified regular expression.
      Monitored Object You can select one of the following types of object:
      • Source IP
      • Header
      • Domain
      • URL Parameter
      Interval Set a time period during which request statistics are collected. This parameter takes effect only if you specify a monitored object. The time period must be 10 seconds to 600 seconds.
      Match Criteria Click Add Criteria and set the following parameters: Type, Parameter, Logical Operator, and Value.
      Note The number of requests that match the specified rule is counted on each edge node. It may take some time to trigger the rate liming rule. You can send more requests to the CDN edge nodes to trigger the rule.
      Action Specify an action to be performed after a request matches the specified match rule. You can select Block or Bot Detection.
      • Block

        If this action is triggered, an HTTP 403 status code is returned to the request.

      • Bot Detection

        If this action is triggered, an HTTP 200 status code is returned to the request and the request is redirected for verification. The request is allowed to access the requested resources only if it passes the verification.

        For example, if an IP address initiates requests more than five times within 20 seconds, bot detection is triggered. All requests from the IP address within the following 10 minutes are verified. Requests from this IP address are allowed to access resources only if the requests pass human-machine identification.

      TTL Specify the time period that IP addresses remain blocked. The time period must be at least 60 seconds.
    3. Click OK.

Examples

The following table provides examples of how to create a custom rule.
Note Specify a value for N based on your business requirements.
Scenario Checked object Interval Match Criteria Action TTL
4xx or 5xx errors IP 10 seconds "status_ratio|404">60%&&"count">50 Block 10 minutes
Queries per second (QPS) anomalies Domain name 10 seconds "count">N Bot Detection 10 minutes