# 使用 Lambda 处理应用程序负载均衡器请求
<a name="services-alb"></a>

您可以使用 Lambda 函数，处理来自 Application Load Balancer 的请求。Elastic Load Balancing 支持 Lambda 函数作为 Application Load Balancer 的目标。使用负载均衡器规则，基于路径或标头值将 HTTP 请求路由到一个函数。处理请求并从 Lambda 函数返回 HTTP 响应。

Elastic Load Balancing 将使用包含请求体和元数据的事件同步调用 Lambda 函数。

**Example Application Load Balancer 请求事件**  

```
{
    "requestContext": {
        "elb": {
            "targetGroupArn": "arn:aws:elasticloadbalancing:us-east-1:123456789012:targetgroup/lambda-279XGJDqGZ5rsrHC2Fjr/49e9d65c45c6791a"
        }
    },
    "httpMethod": "GET",
    "path": "/lambda",
    "queryStringParameters": {
        "query": "1234ABCD"
    },
    "headers": {
        "accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8",
        "accept-encoding": "gzip",
        "accept-language": "en-US,en;q=0.9",
        "connection": "keep-alive",
        "host": "lambda-alb-123578498.us-east-1.elb.amazonaws.com",
        "upgrade-insecure-requests": "1",
        "user-agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36",
        "x-amzn-trace-id": "Root=1-5c536348-3d683b8b04734faae651f476",
        "x-forwarded-for": "72.12.164.125",
        "x-forwarded-port": "80",
        "x-forwarded-proto": "http",
        "x-imforwards": "20"
    },
    "body": "",
    "isBase64Encoded": False
}
```

您的函数将处理事件并以 JSON 格式向负载均衡器返回响应文档。Elastic Load Balancing 将文档转换为 HTTP 成功或错误响应并将其返回给用户。

**Example 响应文档格式**  

```
{
    "statusCode": 200,
    "statusDescription": "200 OK",
    "isBase64Encoded": False,
    "headers": {
        "Content-Type": "text/html"
    },
    "body": "<h1>Hello from Lambda!</h1>"
}
```

要将 Application Load Balancer 配置为函数触发器，请为 Elastic Load Balancing 授予运行函数的权限、创建向函数发送请求的目标组、并将规则添加到向目标组发送请求的负载均衡器。

使用 `add-permission` 命令将权限语句添加到函数的基于资源的策略。

```
aws lambda add-permission --function-name alb-function \
--statement-id load-balancer --action "lambda:InvokeFunction" \
--principal elasticloadbalancing.amazonaws.com
```

您应看到以下输出：

```
{
    "Statement": "{\"Sid\":\"load-balancer\",\"Effect\":\"Allow\",\"Principal\":{\"Service\":\"elasticloadbalancing.amazonaws.com\"},\"Action\":\"lambda:InvokeFunction\",\"Resource\":\"arn:aws:lambda:us-west-2:123456789012:function:alb-function\"}"
}
```

有关配置 Application Load Balancer 侦听器和目标组的说明，请参阅 *Application Load Balancer 用户指南*中的 [Lambda 函数目标](https://docs.aws.amazon.com/elasticloadbalancing/latest/application/lambda-functions.html)。

## Powertools for AWS Lambda 中的事件处理程序
<a name="services-alb-powertools"></a>

在编写由应用程序负载均衡器调用的 Lambda 函数时，Powertools for AWS Lambda 工具包中的事件处理程序提供路由、中间件、CORS 配置、OpenAPI 规范生成、请求验证、错误处理和其他有用的功能。事件处理程序实用程序适用于 Python。有关更多信息，请参阅 *Powertools for AWS Lambda (Python) 文档*中的[事件处理程序 REST API](https://docs.powertools.aws.dev/lambda/python/latest/core/event_handler/api_gateway/)。

### Python
<a name="services-alb-powertools-python"></a>

```
import requests
from requests import Response

from aws_lambda_powertools import Logger, Tracer
from aws_lambda_powertools.event_handler import ALBResolver
from aws_lambda_powertools.logging import correlation_paths
from aws_lambda_powertools.utilities.typing import LambdaContext

tracer = Tracer()
logger = Logger()
app = ALBResolver()


@app.get("/todos")
@tracer.capture_method
def get_todos():
    todos: Response = requests.get("https://jsonplaceholder.typicode.com/todos")
    todos.raise_for_status()

    # for brevity, we'll limit to the first 10 only
    return {"todos": todos.json()[:10]}


# You can continue to use other utilities just as before
@logger.inject_lambda_context(correlation_id_path=correlation_paths.APPLICATION_LOAD_BALANCER)
@tracer.capture_lambda_handler
def lambda_handler(event: dict, context: LambdaContext) -> dict:
    return app.resolve(event, context)
```