👻 Ghoster

In this project, I implemented a simple server-less application for executing Golang functions. Ghoster is a FaaS(Function as a Service) application. As the name suggests, it executes Golang functions on demand. Ghoster is a minimal version of server-less applications like AWS lambda. My purpose in creating this application is to take a deep dive into server-less systems. At this moment, Ghoster can handle simple Golang projects. It cannot handle complex applications like web/HTTP servers, etc.

The way it works is like a layered system. It contains an HTTP server in order to handle user requests, a metrics server to export Ghoster Prometheus metrics, a file server for managing functions/projects, and an exec component for handling FaaS requests.

Run Ghoster using Docker

In order to execute Ghoster, you need to set some environment variables, mount the functions directory (it will be used by file server and exec component in order to do the FaaS logic), and build the application docker image.

env variables

As you can see in the below table, in order to configure a Ghoster, you have to set the following environmental variables.

Name	Description	Type	Example value
`HTTP_PORT`	Ghoster gateway port	integer	8080
`FILE_SERVER_PORT`	File server port	integer	8081
`METRICS_PORT`	Metrics exporter port	integer	8082
`METRICS_NS`	Metrics namespace	string	default
`METRICS_SS`	Metrics subsystem	string	ghoster
`POOL_SIZE`	Number of Ghoster concurrent workers	integer	10
`GC_INTERVAL`	Garbage collector interval in seconds	integer	120

functions dir mount

Ghoster stores Golang projects in a directory called functions. The file server write new functions in this directory, and the exec component loads each function from this directory. Therefore, make sure to mount this directory.

Each project needs to have a main.go, go.mod, and README.md. The readme file will be the description of each function. A suggested project structure is like this:

|_ internal/
|_ pkg/
|_ main.go
|_ go.mod
|_ go.sum
|_ README.md

When you want to upload a new function, make sure to use file server and upload your project as a .zip format.

docker command

In order to build and run Ghoster using docker, you can use the two following commands:

docker pull ghcr.io/amirhnajafiz/ghoster:latest
docker run -d -it -e HTTP_PORT=8080 -p 8080:8080 -v $(pwd)/functions:/var/ghoster/functions ghcr.io/amirhnajafiz/ghoster:latest

Interface

Ghoster uses HTTP requests for registring projects, listing projects, and executing them. In this section we are going to give you some examples in curl in order to work with Ghoster.

upload a new function

curl -i -X POST \
  -F "file_name=subtraction" \
  -F "file=@Archive.zip" \
  localhost:8001/files

list functions

curl -i -X GET localhost:8080/functions

get function description

curl -i -X GET localhost:8080/functions/{function-name}

execute a function

curl -i -X POST -H 'Content-type: application/json' -d '{"args": ["10", "2"]}' localhost:8080/functions/{function-name}

Input params are in JSON format. The args field is an array of input arguments to the function.

Metrics

Ghoster Prometheus metrics are exported in an exporter. You can get them from localhost:8002/metrics.

Suggestions

As mentioned before, Ghoster cannot handle complex functions like HTTP servers. Therefore, it might be good to work on exec component in order to handle complex application. Ghoster resource management is dependent on Go-routines. As they cannot handle some cases, it is a good idea to handle functions used resources.