问题描述

使用Azure API Management, 想对一些固定的IP地址进行访问次数的限制，如被限制的IP地址一分钟可以访问10次，而不被限制的IP地址则可以无限访问？

ChatGPT 解答

最近ChatGPT爆火，所以也把这个问题让ChatGPT来解答，然后人工验证它的回答正确与否？

根据对APIM Policy的文档参考， choose 和 rate-limit 策略组合理论上的确可以实现要求, 接下来就让我们实际验证：

choose策略：Azure API 管理策略参考 | Azure Docs ，choose 策略根据布尔表达式的求值结果应用括住的策略语句，类似于编程语言中的 if-then-else 或开关构造。
rate-limit策略：Azure API 管理策略参考 | Azure Docs ， rate-limit 策略可以对调用速率进行限制，使每个指定时段的调用不超出指定的数目，避免单个订阅的 API 使用量暴增。超过调用速率时，调用方会收到 429 Too Many Requests 响应状态代码。

验证步骤

1）在API的Inbound 策略中添加 choose策略

（策略具体内容，见文末）

2) 测试验证，连续对该API访问10次以上，得到429 Too Many Requests错误

3）以上证明，ChatGPT针对这个问题的解答是正确的！

工程师解答

在参考ChatGPT给出的 choose + rate limit 组合后，我们也发现另一个选项。使用 rate-limit-by-key 策略实现对特定IP的速率限制。

rate-limit-by-key 策略：Azure API 管理策略参考 | Azure Docs ，可以对调用速率进行限制，使指定时段的调用不超出指定的数目，避免单个密钥的 API 使用量暴增。密钥的值可以是任意字符串，通常使用策略表达式来提供密钥。可以添加可选增量条件，指定在决定是否到达限制值时应该进行计数的请求。超过此调用速率时，调用方会收到 429 Too Many Requests 响应状态代码。

在官方文档中给出的示例中，是针对所有的IP(context.Request.IpAddress)都进行了10次/60秒请求的限制，而本示例中则特指“某些固定IP”限制。那么如何来完成这个需求呢？

答案就在“rate-limit-by-key 策略”的说明中，”可以添加可选增量条件，指定在决定是否到达限制值时应该进行计数的请求”, 所以，只要可选增量条件(increment-condition) 的值根据输入的IP地址动态赋值True/False，就能完美匹配以上要求。

理论推断，只需要实现如下逻辑，即可以实现终极需求“想对一些固定的IP地址进行访问次数的限制，如被限制的IP地址一分钟可以访问10次，而不被限制的IP地址则可以无限访问？”

只需两步:

1）通过设置一个变量(set-variable) 值，用C#代码来计算变量值，在赋值语句中，预先定义一个IP限制列表，通过 contains 检查当前请求IP是否在列表中，返回True or False 。True表示当前请求的IP需要速率限制, 否则，不需要。

2）然后，在rate-limit-by-key 的 increment-condition条件中使用上一步参数值，进行判断是否计入限制

验证步骤

1）在API的 Inbound 策略中添加 rate-limit-by-key策略

（策略具体内容，见文末）

2）验证在30秒，访问5次以上后，同样得到429 Too Many Requests错误

3) 当在请求Headers中添加Ocp-Apim-Trace: true 和 Ocp-Apim-Subscription-Key: {订阅Key}后，可以查看请求在APIM中执行的日志跟踪。可以查看rate-limit-by-key 策略的执行情况.

总结

想实现固定IP地址访问次数的限制，至少有如下两种解决方案。

方案一：Choose + rate-limit 策略组合

<!--
    IMPORTANT:
    - Policy elements can appear only within the <inbound>, <outbound>, <backend> section elements.
    - To apply a policy to the incoming request (before it is forwarded to the backend service), place a corresponding policy element within the <inbound> section element.
    - To apply a policy to the outgoing response (before it is sent back to the caller), place a corresponding policy element within the <outbound> section element.
    - To add a policy, place the cursor at the desired insertion point and select a policy from the sidebar.
    - To remove a policy, delete the corresponding policy statement from the policy document.
    - Position the <base> element within a section element to inherit all policies from the corresponding section element in the enclosing scope.
    - Remove the <base> element to prevent inheriting policies from the corresponding section element in the enclosing scope.
    - Policies are applied in the order of their appearance, from the top down.
    - Comments within policy elements are not supported and may disappear. Place your comments between policy elements or at a higher level scope.
-->
<policies>
    <inbound>
        <base />
        <set-variable name="IsCountIpLimit" value="@{
                string ipAddress =context.Request.IpAddress; 

                List<string> cidrList = new List<string>(){
                    "167.xxx. xxx.135",
                    "167.xxx. xxx.136",
                    "167.xxx. xxx.137"
                };
                return cidrList.Contains(ipAddress);
                }" />
        <choose>
            <when condition="@((bool)context.Variables["IsCountIpLimit"])">
                <rate-limit calls="10" renewal-period="60" />
            </when>
        </choose>
    </inbound>
    <backend>
        <base />
    </backend>
    <outbound>
        <base />
    </outbound>
    <on-error>
        <base />
    </on-error>
</policies>

方案二：rate-limit-by-key策略

<!--
    IMPORTANT:
    - Policy elements can appear only within the <inbound>, <outbound>, <backend> section elements.
    - To apply a policy to the incoming request (before it is forwarded to the backend service), place a corresponding policy element within the <inbound> section element.
    - To apply a policy to the outgoing response (before it is sent back to the caller), place a corresponding policy element within the <outbound> section element.
    - To add a policy, place the cursor at the desired insertion point and select a policy from the sidebar.
    - To remove a policy, delete the corresponding policy statement from the policy document.
    - Position the <base> element within a section element to inherit all policies from the corresponding section element in the enclosing scope.
    - Remove the <base> element to prevent inheriting policies from the corresponding section element in the enclosing scope.
    - Policies are applied in the order of their appearance, from the top down.
    - Comments within policy elements are not supported and may disappear. Place your comments between policy elements or at a higher level scope.
-->
<policies>
    <inbound>
        <base />
        <set-variable name="IsCountIpLimit" value="@{
                string ipAddress =context.Request.IpAddress; 

                List<string> limitIPs = new List<string>(){
                    "167.xxx. xxx.135",
                    "167.xxx. xxx.136",
                    "167.xxx. xxx.137"
                };

                return limitIPs.Contains(ipAddress);
                }" />
        <rate-limit-by-key calls="5" renewal-period="30" counter-key="@(context.Request.IpAddress)" increment-condition="@(context.Response.StatusCode >= 200 && context.Response.StatusCode < 300 && (bool)context.Variables["IsCountIpLimit"])" />
    </inbound>
    <backend>
        <base />
    </backend>
    <outbound>
        <base />
    </outbound> 
    <on-error>
        <base />
    </on-error>
</policies>