Examples: Add hello world.

Signed-off-by: Antony MECHIN <[email protected]>

Author: Antony MECHIN

examples/hello-world/README.md

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+## The Docker voting app
+
+### Initialize project
+
+In this example, we will create a one-service application that deploys an web page displaying a message.
+
+Initialize the project using `docker-app init hello-world`.
+
+### Edit metadata
+
+Go to `hello-world.dockerapp/` and open `metadata.yml` and fill the following fields:
+- description
+- maintainers
+
+### Add variables to the compose file
+
+Open `docker-compose.yml` and add a service `hello`.
+
+```
+services:
+  hello:
+    image: hashicorp/http-echo
+    command: ["-text", "${text}"]
+    ports:
+      - ${port}:5678
+```
+
+### Give variables their default value
+
+Open `settings.yml` and every variables with the default value you want, e.g.:
+
+```
+$ cat settings.yml
+port: 8080
+text: world
+```
+
+### Render
+
+You can now render your application by running `docker-app render` or even personalize the rendered compose file by running `docker-app render -s text="hello user"`.
+
+Create a `render` directory and redirect the output of `docker-app render ...` to `render/docker-compose.yml`.
+
+```
+mkdir -p render
+docker-app render -s text="hello user" > render/docker-compose.yml
+```
+
+### Deploy
+
+Deploy your application by running `docker-app deploy -c render/docker-compose.yml`. http://<ip_of_your_node>:8080 will display your message, e.g. http://127.0.0.1:8080 if you deployed locally.

examples/hello-world/hello-world.dockerapp/docker-compose.yml

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+version: "3.3"
+services:
+  hello:
+    image: hashicorp/http-echo
+    command: ["-text", "${text}"]
+    ports:
+      - ${port}:5678

examples/hello-world/hello-world.dockerapp/metadata.yml

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+version: 0.1.0
+name: echo
+description: "Hello world"
+maintainers:
+- name: dimrok
+  email: "[email protected]"
+targets:
+  swarm: true
+  kubernetes: true

examples/hello-world/hello-world.dockerapp/settings.yml

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+port: 8080
+text: world