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Add a helloworld sample for haskell (#316) 

* Add a helloworld sample for haskell

* Use stack as the build tool
* Use scotty as a web framework
* Use docker multi-stage build to create a smaller runtime image

* Apply review comments on the README.md

* Apply language review comments

- Fix `service.yaml` indentation
- Change heading for sample code recreation
This commit is contained in:
Gaurav Abbi 2018-08-21 18:07:58 +02:00 committed by Knative Prow Robot
parent 1a48e0bbe8
commit 1b52510c44
7 changed files with 280 additions and 0 deletions
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.stack-work/
*.cabal
*~
/.idea/
/dist/
/out/

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# Use the existing Haskell image as our base
FROM haskell:8.2.2 as builder
# Checkout our code onto the Docker container
WORKDIR /app
ADD . /app
# Build and test our code, then install the “helloworld-haskell-exe” executable
RUN stack setup
RUN stack build --copy-bins
# Copy the "helloworld-haskell-exe" executable to the image using docker multi stage build
FROM fpco/haskell-scratch:integer-gmp
WORKDIR /root/
COPY --from=builder /root/.local/bin/helloworld-haskell-exe .
# Expose a port to run our application
EXPOSE 8080
# Run the server command
CMD ["./helloworld-haskell-exe"]

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# Hello World - Haskell sample
A simple web app written in Haskell that you can use for testing.
It reads in an env variable `TARGET` and prints "Hello World: ${TARGET}!". If
TARGET is not specified, it will use "NOT SPECIFIED" as the TARGET.
## Prerequisites
* A Kubernetes cluster with Knative installed. Follow the
[installation instructions](https://github.com/knative/docs/blob/master/install/README.md) if you need
to create one.
* [Docker](https://www.docker.com) installed and running on your local machine,
and a Docker Hub account configured (we'll use it for a container registry).
## Recreating the sample code
While you can clone all of the code from this directory, hello world
apps are generally more useful if you build them step-by-step. The
following instructions recreate the source files from this folder.
1. Create a new file named `stack.yaml` and paste the following code:
```yaml
flags: {}
packages:
- .
extra-deps: []
resolver: lts-10.7
```
1. Create a new file named `package.yaml` and paste the following code
```yaml
name: helloworld-haskell
version: 0.1.0.0
dependencies:
- base >= 4.7 && < 5
- scotty
- text
executables:
helloworld-haskell-exe:
main: Main.hs
source-dirs: app
ghc-options:
- -threaded
- -rtsopts
- -with-rtsopts=-N
```
1. Create a `app` folder, then create a new file named `Main.hs` in that folder
and paste the following code. This code creates a basic web server which
listens on port 8080:
```haskell
{-# LANGUAGE OverloadedStrings #-}
import Data.Maybe
import Data.Monoid ((<>))
import Data.Text.Lazy (Text)
import Data.Text.Lazy
import System.Environment (lookupEnv)
import Web.Scotty (ActionM, ScottyM, scotty)
import Web.Scotty.Trans
main :: IO ()
main = do
t <- fromMaybe "NOT SPECIFIED" <$> lookupEnv "TARGET"
scotty 8080 (route t)
route :: String -> ScottyM()
route t = get "/" $ hello t
hello :: String -> ActionM()
hello t = text $ pack ("Hello world: " ++ t)
```
1. In your project directory, create a file named `Dockerfile` and copy the code
block below into it.
```docker
# Use the existing Haskell image as our base
FROM haskell:8.2.2 as builder
# Checkout our code onto the Docker container
WORKDIR /app
ADD . /app
# Build and test our code, then install the “helloworld-haskell-exe” executable
RUN stack setup
RUN stack build --copy-bins
# Copy the "helloworld-haskell-exe" executable to the image using docker multi stage build
FROM fpco/haskell-scratch:integer-gmp
WORKDIR /root/
COPY --from=builder /root/.local/bin/helloworld-haskell-exe .
# Expose a port to run our application
EXPOSE 8080
# Run the server command
CMD ["./helloworld-haskell-exe"]
```
1. Create a new file, `service.yaml` and copy the following service definition
into the file. Make sure to replace `{username}` with your Docker Hub username.
```yaml
apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:
name: helloworld-haskell
namespace: default
spec:
runLatest:
configuration:
revisionTemplate:
spec:
container:
image: docker.io/{username}/helloworld-haskell
env:
- name: TARGET
value: "Haskell Sample v1"
```
## Build and deploy this sample
Once you have recreated the sample code files (or used the files in the sample
folder) you're ready to build and deploy the sample app.
1. Use Docker to build the sample code into a container. To build and push with
Docker Hub, enter these commands replacing `{username}` with your
Docker Hub username:
```shell
# Build the container on your local machine
docker build -t {username}/helloworld-haskell .
# Push the container to docker registry
docker push {username}/helloworld-haskell
```
1. After the build has completed and the container is pushed to Docker Hub, you
can deploy the app into your cluster. Ensure that the container image value
in `service.yaml` matches the container you built in
the previous step. Apply the configuration using `kubectl`:
```shell
kubectl apply -f service.yaml
```
1. Now that your service is created, Knative will perform the following steps:
* Create a new immutable revision for this version of the app.
* Network programming to create a route, ingress, service, and load balance for your app.
* Automatically scale your pods up and down (including to zero active pods).
1. To find the IP address for your service, enter
`kubectl get svc knative-ingressgateway -n istio-system` to get the ingress IP for your
cluster. If your cluster is new, it may take some time for the service to get assigned
an external IP address.
```shell
kubectl get svc knative-ingressgateway -n istio-system
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
knative-ingressgateway LoadBalancer 10.23.247.74 35.203.155.229 80:32380/TCP,443:32390/TCP,32400:32400/TCP 2d
```
For minikube or bare-metal, get IP_ADDRESS by running the following command
```shell
echo $(kubectl get node -o 'jsonpath={.items[0].status.addresses[0].address}'):$(kubectl get svc knative-ingressgateway -n istio-system -o 'jsonpath={.spec.ports[?(@.port==80)].nodePort}')
```
1. To find the URL for your service, enter:
```
kubectl get services.serving.knative.dev helloworld-haskell -o=custom-columns=NAME:.metadata.name,DOMAIN:.status.domain
NAME DOMAIN
helloworld-haskell helloworld-haskell.default.example.com
```
1. Now you can make a request to your app and see the result. Replace
`{IP_ADDRESS}` with the address you see returned in the previous step.
```shell
curl -H "Host: helloworld-haskell.default.example.com" http://{IP_ADDRESS}
Hello world: Haskell Sample v1
```
## Removing the sample app deployment
To remove the sample app from your cluster, delete the service record:
```shell
kubectl delete -f service.yaml
```

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{-# LANGUAGE OverloadedStrings #-}
import Data.Maybe
import Data.Monoid ((<>))
import Data.Text.Lazy (Text)
import Data.Text.Lazy
import System.Environment (lookupEnv)
import Web.Scotty (ActionM, ScottyM, scotty)
import Web.Scotty.Trans
main :: IO ()
main = do
t <- fromMaybe "NOT SPECIFIED" <$> lookupEnv "TARGET"
scotty 8080 (route t)
route :: String -> ScottyM()
route t = get "/" $ hello t
hello :: String -> ActionM()
hello t = text $ pack ("Hello world: " ++ t)

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name: helloworld-haskell
version: 0.1.0.0
dependencies:
- base >= 4.7 && < 5
- scotty
- text
executables:
helloworld-haskell-exe:
main: Main.hs
source-dirs: app
ghc-options:
- -threaded
- -rtsopts
- -with-rtsopts=-N

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apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:
name: helloworld-haskell
namespace: default
spec:
runLatest:
configuration:
revisionTemplate:
spec:
container:
image: docker.io/{username}/helloworld-haskell
env:
- name: TARGET
value: "Haskell Sample v1"

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flags: {}
packages:
- .
extra-deps: []
resolver: lts-10.7