After playing around with some OpenFaas functions I came across the alexellis/mongodb-function. After reading through the README and having a play around with it I thought I would have a go at porting it to C# using .Net Core. Not only did I do this for a personal challenge but I also thought it could be useful to others who prefer to develop using C#/.Net Core.



This function creates a connection to a MongoDB and maintains the connection for the lifetime of the function. This means that a cold start, time taken to create the connection, will only occur on the initial request. Therefore all successive requests are relatively fast.

The csharp-kestrel-mongo project is the result. This OpenFaas function template when created provides you with a function handler for which you can interact with a MongoDB. The function offers you the ability to specify environment variables that defines your MongoDB instance(s).

It follows a slightly different design architecture compared to the one described in the original mongodb-function.

Credit: Alex Ellis’ original template architecture https://github.com/alexellis/mongodb-function modified for this template

If you are familiar with OpenFaas, a quick rundown on how to get up and running with this function follows using Play with Docker (A free online docker playground).

If you are using Play with Docker, create a Docker instance and install OpenFaas following the Docker Swarm instructions specified on the OpenFaas docs, otherwise you can follow along with your own OpenFaas deployment. You will also need access to a MongoDB. If you are following along using Play with Docker this can be done by running the following Docker commands in your instance:

docker volume create mongodata



docker run --name mongodb -d -p 27017:27017 -v mongodata:/data/db mongo mongod

Once completed the MongoDB function can be downloaded and created:

faas-cli template pull https://github.com/Marcus-Smallman/csharp-kestrel-mongo.git



faas-cli new mongo-function --lang csharp-kestrel-mongo

Note: armhf is also supported so you can deploy this function to your raspberry pi(s)! Simply change the specified language to csharp-kestrel-mongo-armhf

This will pull the template and create a new function called ‘mongo-function’. A mongo-function.yml file will be created which is required to deploy your function. This file allows for environment variables to be set that your function can access. An environment variable called mongo_endpoint is required for this function which specifies where your MongoDB is accessible from. There are also some extra optional environment variables that can be set.

An example of the modified mongo_function.yml file follows:



provider:

name: faas

gateway: http://127.0.0.1:8080



functions:

mongo-function:

lang: csharp-kestrel-mongo

handler: ./mongo-function

image: <docker-registry>/mongo-function

environment:

mongo_endpoint: <your-mongo-endpoint>:27017

mongo_database_name: my_mongo_database

mongo_collection_name: my_mongo_collection

Note: Don’t forget to modify your gateway address! I always forget to do this.

If you are following along with Play with Docker replace the <your-mongo-endpoint> with the IP of the docker instance created and replace the gateway value to your OpenFaas endpoint (the URL). As you will be also be building and pushing this function to a docker registry, you will need to make sure that <docker-registry> is replaced with the one you will use for this function.

Now that we have everything set up we can get to the fun part, the actual function logic! This will all be done in the generated FunctionHandler.cs file:

public class FunctionHandler

{

public Task < string > Handle ( object input )

{

this . GetCollection ()

. InsertOne ( input . ToBsonDocument ());



var response = new ResponseModel ()

{

response = input ,

status = 201

};



return Task . FromResult ( JsonConvert . SerializeObject ( response ));

}

}

By default the template inserts the request body into MongoDB and returns a response object with the provided input and a HTTP status code of 201. This can of course be changed to do anything you want from creating new MongoDB collection to updating all documents that contain the value OpenFaas. The function can then be deployed:

faas-cli build -f mongo-function.yml



faas-cli push -f mongo-function.yml



faas-cli deploy -f mongo-function.yml

To access and play around with the function we can head over to the OpenFaas gateway UI:

Data can then be sent via the request body to the function as seen in the screen shot above. This will then, if successful, return your given input and a status code of 201.

We can also prove that the data has been written to our MongoDB by using a MongoDB client to connect to our MongoDB and check that the data has been stored:

Cool, huh?

For more technical and in depth usage of the function template please read the documentation described in the project repository.

GitHub project: csharp-kestrel-mongo

– Marcus

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