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https://github.com/sourcedennis/aws-lambda-z3

A tutorial on running Z3 on AWS Lambda, with Rust
https://github.com/sourcedennis/aws-lambda-z3

aws-lambda z3

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A tutorial on running Z3 on AWS Lambda, with Rust

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# aws-lambda-z3



A *Tutorial* on setting up the [Z3 theorem prover](https://github.com/Z3Prover/z3), for use within a Rust program, within [AWS Lambda](https://aws.amazon.com/lambda/). The tutorial is mostly for myself, as I'll have forgotten this in two weeks. Hopefully it is useful for others too.



This Rust project is merely a *proof-of-concept*. It performs:



* Take a HTTP POST request with a value, in JSON (formatted as `{"val": 42}`).

* Invokes Z3 to find two non-zero positive integers `x` and `y` (which are less than `val`), which sum to `val`.

  * That is, `x > 0`, `y > 0`, `x < val`, `y < val`, `x + y = val`

* In the HTTP response, it returns those values, as JSON. (formatted as `{"x":6,"y":36}`).



Note that Z3 is a *dynamically linked* dependency of our program, which needs to be shipped along. To accomplish that, we pack everything into a Docker image, which we push to AWS.



The contents of both `src/main.rs` and `Dockerfile` are documented. The remainder of this README elaborates on getting the project into Lambda.



## Build the Docker image



Simply run:



```

docker build . --tag=aws-lambda-z3

```



Note that this pull [Z3 from GitHub](https://github.com/Z3Prover/z3) and builds it from scratch. This may take a while.



## Push the Docker image to AWS



* Create a Docker repository on [Amazon ECR](https://console.aws.amazon.com/ecr/home/).

* Push the image to the repository

  * Inside the repository (in AWS console), follow the instructions described in **View push commands**.



## Creating the Lambda Function



* Go to the [AWS Lambda Console](https://console.aws.amazon.com/lambda/home)

* Click **Create function**

* Select **Container image**

* Give your function a name (e.g., `aws-lambda-z3`)

* Select your pushed image in the **Container image URI** field



## Make the Function publicly accessible



* Click **+ Add trigger**

* Select for API: **Create an API**

* Select for API type: **REST API**

* Select for Security: **Open**

* Keep the default "Additional settings"

* Click **Add**



AWS offers Lambda Proxy Integration, which seemingly interferes with our program's ability to parse a request. For simplicity, disable it:



* Go to the [Amazon API Gateway Console](https://console.aws.amazon.com/apigateway/home)

* Select **Integration Request**

* **Uncheck** the box for **Use Lambda Proxy Integration**

* **Important!** Click `Actions > Deploy API` and redeploy to the default stage



Now the program should be publicly accessible through an URL - as listed in Lambda's trigger information. This URL looks like:

```

https://*.execute-api.*.amazonaws.com/default/aws-lambda-z3

```



## Testing



To test the Lambda function, make a POST request with (replace `[URL]`):

```

curl -X POST -d '{"val": 42}' "[URL]"

```

This should return:

```

{"x":6,"y":36}

```



Note that the [Amazon API Gateway Console](https://console.aws.amazon.com/apigateway/home) also offers utilities to perform HTTP requests.



Well done! Now you have Z3 running inside Lambda.



## Common Errors



While setting this up, I ran into several HTTP errors:



* `403` - Forbidden. This likely occurs when you've sent the request *to the wrong URL*.

* `500`/`502` - Internal Server Error. This happens when the program crashes. Possibly because the JSON string does not contain the `val` field. Alternatively, make sure *Lambda Proxy Integration* is disabled (and then redeploy); As it seemingly modifies the input JSON message.



## License



BSD-3 - See the `LICENSE` file