# Using Amazon WAF to protect your Amazon AppSync APIs
Amazon WAF is a web application firewall that helps protect web applications and APIs from attacks. It allows you to configure a set of rules, called a web access control list (web ACL), that allow, block, or monitor (count) web requests based on customizable web security rules and conditions that you define. When you integrate your Amazon AppSync API with Amazon WAF, you gain more control and visibility into the HTTP traffic accepted by your API. To learn more about Amazon WAF, see [How Amazon WAF Works](https://docs.amazonaws.cn/waf/latest/developerguide/how-aws-waf-works.html) in the Amazon WAF Developer Guide.
You can use Amazon WAF to protect your AppSync API from common web exploits, such as SQL injection and cross-site scripting (XSS) attacks. These could affect API availability and performance, compromise security, or consume excessive resources. For example, you can create rules to allow or block requests from specified IP address ranges, requests from CIDR blocks, requests that originate from a specific country or region, requests that contain malicious SQL code, or requests that contain malicious script.
You can also create rules that match a specified string or a regular expression pattern in HTTP headers, method, query string, URI, and the request body (limited to the first 8 KB). Additionally, you can create rules to block attacks from specific user agents, bad bots, and content scrapers. For example, you can use rate-based rules to specify the number of web requests that are allowed by each client IP in a trailing, continuously updated, 5-minute period.
To learn more about the types of rules that are supported and additional Amazon WAF features, see the [Amazon WAF Developer Guide](https://docs.amazonaws.cn/waf/latest/developerguide/waf-chapter.html) and the [Amazon WAF API Reference](https://docs.amazonaws.cn/waf/latest/APIReference/API_Types_AWS_WAFV2.html).
**Important**
Amazon WAF is your first line of defense against web exploits. When Amazon WAF is enabled on an API, Amazon WAF rules are evaluated before other access control features, such as API key authorization, IAM policies, OIDC tokens, and Amazon Cognito user pools.
## Integrate an AppSync API with Amazon WAF
You can integrate an Appsync API with Amazon WAF using the Amazon Web Services Management Console, the Amazon CLI, Amazon CloudFormation, or any other compatible client.
**To integrate an Amazon AppSync API with Amazon WAF**
1. Create an Amazon WAF web ACL. For detailed steps using the [Amazon WAF Console](https://console.amazonaws.cn/waf/), see [Creating a web ACL](https://docs.amazonaws.cn/waf/latest/developerguide/web-acl-creating.html).
1. Define the rules for the web ACL. A rule or rules are defined in the process of creating the web ACL. For information about how to structure rules, see [Amazon WAF rules](https://docs.amazonaws.cn/waf/latest/developerguide/waf-rules.html). For examples of useful rules you can define for your Amazon AppSync API, see [Creating rules for a web ACL](#Creating-web-acl-rules).
1. Associate the web ACL with an Amazon AppSync API. You can perform this step in the [Amazon WAF Console](https://console.amazonaws.cn/wafv2/) or in the [AppSync Console](https://console.amazonaws.cn/appsync/).
+ To associate the web ACL with an Amazon AppSync API in the Amazon WAF Console, follow the instructions for [Associating or disassociating a Web ACL with an Amazon resource](https://docs.amazonaws.cn/waf/latest/developerguide/web-acl-associating-aws-resource.html) in the Amazon WAF Developer Guide.
+ To associate the web ACL with an Amazon AppSync API in the Amazon AppSync Console
1. Sign in to the Amazon Web Services Management Console and open the [AppSync Console](https://console.amazonaws.cn/appsync/).
1. Choose the API that you want to associate with a web ACL.
1. In the navigation pane, choose **Settings**.
1. In the **Web application firewall** section, turn on **Enable Amazon WAF**.
1. In the **Web ACL** dropdown list, choose the name of the web ACL to associate with your API.
1. Choose **Save** to associate the web ACL with your API.
**Note**
After you create a web ACL in the Amazon WAF Console, it can take a few minutes for the new web ACL to be available. If you do not see a newly created web ACL in the **Web application firewall** menu, wait a few minutes and retry the steps to associate the web ACL with your API.
**Note**
Amazon WAF integration only supports the `Subscription registration message` event for real-time endpoints. Amazon AppSync will respond with an error message instead of a `start_ack` message for any `Subscription registration message` blocked by Amazon WAF.
After you associate a web ACL with an Amazon AppSync API, you will manage the web ACL using the Amazon WAF APIs. You do not need to re-associate the web ACL with your Amazon AppSync API unless you want to associate the Amazon AppSync API with a different web ACL.
## Creating rules for a web ACL
Rules define how to inspect web requests and what to do when a web request matches the inspection criteria. Rules don't exist in Amazon WAF on their own. You can access a rule by name in a rule group or in the web ACL where it's defined. For more information, see [Amazon WAF rules](https://docs.amazonaws.cn/waf/latest/developerguide/waf-rules.html). The following examples demonstrate how to define and associate rules that are useful for protecting an AppSync API.
**Example web ACL rule to limit request body size**
The following is an example of a rule that limits the body size of requests. This would be entered into the **Rule JSON editor** when creating a web ACL in the Amazon WAF Console.
```
{
"Name": "BodySizeRule",
"Priority": 1,
"Action": {
"Block": {}
},
"Statement": {
"SizeConstraintStatement": {
"ComparisonOperator": "GE",
"FieldToMatch": {
"Body": {}
},
"Size": 1024,
"TextTransformations": [
{
"Priority": 0,
"Type": "NONE"
}
]
}
},
"VisibilityConfig": {
"CloudWatchMetricsEnabled": true,
"MetricName": "BodySizeRule",
"SampledRequestsEnabled": true
}
}
```
After you have created your web ACL using the preceding example rule, you must associate it with your AppSync API. As an alternative to using the Amazon Web Services Management Console, you can perform this step in the Amazon CLI by running the following command.
```
aws waf associate-web-acl --web-acl-id waf-web-acl-arn --resource-arn appsync-api-arn
```
It can take a few minutes for the changes to propagate, but after running this command, requests that contain a body larger than 1024 bytes will be rejected by Amazon AppSync.
After you create a new web ACL in the Amazon WAF Console, it can take a few minutes for the web ACL to be available to associate with an API. If you run the CLI command and get a `WAFUnavailableEntityException` error, wait a few minutes and retry running the command.
**Example web ACL rule to limit requests from a single IP address**
The following is an example of a rule that throttles an AppSync API to 100 requests from a single IP address. This would be entered into the **Rule JSON editor** when creating a web ACL with a rate-based rule in the Amazon WAF Console.
```
{
"Name": "Throttle",
"Priority": 0,
"Action": {
"Block": {}
},
"VisibilityConfig": {
"SampledRequestsEnabled": true,
"CloudWatchMetricsEnabled": true,
"MetricName": "Throttle"
},
"Statement": {
"RateBasedStatement": {
"Limit": 100,
"AggregateKeyType": "IP"
}
}
}
```
After you have created your web ACL using the preceding example rule, you must associate it with your AppSync API. You can perform this step in the Amazon CLI by running the following command.
```
aws waf associate-web-acl --web-acl-id waf-web-acl-arn --resource-arn appsync-api-arn
```
**Example web ACL rule to prevent GraphQL \$1\$1schema introspection queries to an API**
The following is an example of a rule that prevents GraphQL \$1\$1schema introspection queries to an API. Any HTTP body that includes the string "\$1\$1schema" will be blocked. This would be entered into the **Rule JSON editor** when creating a web ACL in the Amazon WAF Console.
```
{
"Name": "BodyRule",
"Priority": 5,
"Action": {
"Block": {}
},
"VisibilityConfig": {
"SampledRequestsEnabled": true,
"CloudWatchMetricsEnabled": true,
"MetricName": "BodyRule"
},
"Statement": {
"ByteMatchStatement": {
"FieldToMatch": {
"Body": {}
},
"PositionalConstraint": "CONTAINS",
"SearchString": "__schema",
"TextTransformations": [
{
"Type": "NONE",
"Priority": 0
}
]
}
}
}
```
After you have created your web ACL using the preceding example rule, you must associate it with your AppSync API. You can perform this step in the Amazon CLI by running the following command.
```
aws waf associate-web-acl --web-acl-id waf-web-acl-arn --resource-arn appsync-api-arn
```