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## Develop your own function
### TestDrive
Before you start development, you may want to take FaaS for a test drive which sets up a stack of sample functions from docker-compose.yml. You can then build your own functions and add them to the stack.
> You can test-drive FaaS with a set of sample functions as defined in docker-compose.yml on play-with-docker.com for free, or on your own laptop.
* [Begin the TestDrive instructions](https://github.com/alexellis/faas/blob/master/TestDrive.md)
### Working on the API Gateway or Watchdog
To work on either of the FaaS Golang components checkout the "./build.sh" scripts and acompanying Dockerfiles.
* [Roadmap and Contributing](https://github.com/alexellis/faas/blob/master/ROADMAP.md)
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### Creating a function
Functions run as Docker containers with the Watchdog component embedded to handle communication with the API Gateway.
**Markdown Parser**
This is the basis of a function which generates HTML from MarkDown:
```
FROM golang:1.7.3
RUN mkdir -p /go/src/app
COPY handler.go /go/src/app
WORKDIR /go/src/app
RUN go get github.com/microcosm-cc/bluemonday && \
go get github.com/russross/blackfriday
RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o app .
ADD https://github.com/alexellis/faas/releases/download/v0.3-alpha/fwatchdog /usr/bin
RUN chmod +x /usr/bin/fwatchdog
ENV fprocess="/go/src/app/app"
CMD ["/usr/bin/watchdog"]
```
The base Docker container is not important, you just need to add the watchdog component and then set the fprocess to execute your binary at runtime.
Update the Docker stack with this:
```
markdown:
image: alexellis2/faas-markdownrender:latest
labels:
function: "true"
depends_on:
- gateway
networks:
- functions
```
**Word counter with busybox**
```
FROM alpine:latest
ADD https://github.com/alexellis/faas/releases/download/v0.3-alpha/fwatchdog /usr/bin
RUN chmod +x /usr/bin/fwatchdog
ENV fprocess="wc"
CMD ["fwatchdog"]
```
Update your Docker stack with this definition:
```
wordcount:
image: alexellis2/faas-alpinefunction:latest
labels:
function: "true"
depends_on:
- gateway
networks:
- functions
environment:
fprocess: "wc"
```
### Testing your function
You can test your function through a webbrowser against the UI portal on port 8080.
http://localhost:8080/
You can also invoke a function by name with curl:
```
curl --data-binary @README.md http://localhost:8080/function/func_wordcount
```