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GH-698 Fix routing function support in AWS

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Introduce auto-fallback to routing function if more then one function is present and no definition is provided.
Add explicit routing sample

Add documentation
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Oleg Zhurakousky
2021-05-19 15:22:57 +02:00
parent 86e141c199
commit 039387d9c6
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spring-cloud-function-samples/function-sample-aws-routing/README.adoc Normal file
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This example demonstrates routing capabilities of spring-cloud-function when deployed as AWS Lambdas.
Usually when you deploy configuration (non-custom runtime) with a single function it is automatically recognized and bound as AWS Lambda
by `org.springframework.cloud.function.adapter.aws.FunctionInvoker` (FunctionInvoker).
However when you have multiple functions present in your configuration you need to tell `FunctionInvoker` the target function definition.
You can do so in two different ways.
1. You can provide `spring_cloud_function_definition` environment variable setting its value to the desired function definition, which could also be composition
(e.g., `spring_cloud_function_definition=foo|bar`).
2. A more dynamic and recommended approach would be to fallback on auto routing capabilities of spring-cloud function's in AWS environment.
Basically every time you have more then one function in your configuration, the framework will bind
[Routing Function](https://docs.spring.io/spring-cloud-function/docs/3.1.3/reference/html/spring-cloud-function.html#_function_routing_and_filtering)
as AWS Lambda, and all you need to to is provide a routing instruction via Message headers or environment variables. The instructions could themselves be very dynamic,
since we support both SpEL and registering a callback interface. For more details on routing mechanisms please refer to
[Function Routing and Filtering](https://docs.spring.io/spring-cloud-function/docs/3.1.3/reference/html/spring-cloud-function.html#_function_routing_and_filtering) section.
NOTE: Keep in mind though that since AWS does not allow dots `.` and/or hyphens`-` in the name of the environment variable, you can benefit from boot support and simply substitute
dots with underscores and hyphens with camel case. So for example `spring.cloud.function.definition` becomes `spring_cloud_function_definition`
and `spring.cloud.function.routing-expression` becomes `spring_cloud_function_routingExpression`.
In this example we have configuration with two functions; `uppercase` and `reverse`.
When executing from AWS Lambda functions dashboard you can simply provide one of the mentioned properties as environment variables via Configuration tab.
For example, you can set `spring_cloud_function_routingExpression` environment variable with the value of literal; SpEL expression `'uppercase'` (not the single quotes).
As for API Gateway, you can also pass routing instructions as Message headers by proving them as HTTP headers.
You can test it with API Gateway dashboard or (once deployed), you can for example POST to it via `curl`.
Here is the example of curl command
```
curl -X POST https://[. . .].execute-api.eu-west-3.amazonaws.com/route/aws-routing-gw -H "spring.cloud.function.definition: uppercase" -H "Content-Type: application/json" -d '"foo"'
```