[step-contents]

{% endhighlight %}

You must define a step type for each step. Each step uses Docker images and containers as facilitators for execution. For example, the[**Freestyle**]({{site.baseurl}}/docs/codefresh-yaml/steps/freestyle/) step spins up a container and executes the specified shell commands from the YAML file.

You must define a step type for each step, unless you are using a[freestyle step]({{site.baseurl}}/docs/codefresh-yaml/steps/freestyle/). Each step uses Docker images and containers as facilitators for execution. For example, the[**Freestyle**]({{site.baseurl}}/docs/codefresh-yaml/steps/freestyle/) step spins up a container and executes the specified shell commands from the YAML file.

The step names should be unique within the same pipeline. This mainly affects the visualization of the pipeline when it runs.

Each step produces a resource, which you can reference in other steps, and are executed in real-time. For example, a[**Freestyle**]({{site.baseurl}}/docs/codefresh-yaml/steps/freestyle/) step can reference an image that was produced by a[**Build**]({{site.baseurl}}/docs/codefresh-yaml/steps/build/) step. This allows you to chain steps together and create highly-customized builds.

Each step produces a resource, which you can[reference](https://github.com/codefresh-contrib/python-flask-sample-app/blob/master/codefresh.yml#L23) in other steps, and are executed in real-time. For example, a[**Freestyle**]({{site.baseurl}}/docs/codefresh-yaml/steps/freestyle/) step can reference an image that was produced by a[**Build**]({{site.baseurl}}/docs/codefresh-yaml/steps/build/) step. This allows you to chain steps together and create highly-customized builds.

<divclass="bd-callout bd-callout-info"markdown="1">

| -----------------------------------------------------------------------------------------------------------------| ----------------------------------------------|

|[Freestyle]({{site.baseurl}}/docs/codefresh-yaml/steps/freestyle/)| Executes one or more shell commands in a container similar to`docker run`.|

|[Build]({{site.baseurl}}/docs/codefresh-yaml/steps/build/)| Builds a Docker image like`docker build`.|

|[Push]({{site.baseurl}}/docs/codefresh-yaml/steps/push/)| Pushes a Docker image toa Docker registry similar to`docker tag` and`docker push`.|

|[Push]({{site.baseurl}}/docs/codefresh-yaml/steps/push/)| Pushes a Docker image toan external registry similar to`docker tag` and`docker push`.|

|[Git Clone]({{site.baseurl}}/docs/codefresh-yaml/steps/git-clone/)| Overrides the default git clone behavior.|

|[Composition]({{site.baseurl}}/docs/codefresh-yaml/steps/composition/)| Starts a Docker Composition like`docker-compose`. Discarded once pipelines finishes.|

|[Launch Composition]({{site.baseurl}}/docs/codefresh-yaml/steps/launch-composition/)| Starts a long term Docker composition that stays up after the end of the pipeline.|

{% highlight shell %}

{% raw %}

$codefresh validate codefresh.yml

$codefresh validate codefresh.yml

Yaml not valid:

- "invalid-property" is not allowed

{% endraw %}

Let’s Chat is self-hosted chat app for small to big teams.

This tutorial will walk you through the process of adding the following:

-`Build step` - that will build docker image for your let’s chat app.

-`Push to registry step` - that will push your image to docker hub.

-`Unit Test step` - A freestyle step that runs the unit test of the demo chat after the build.

-`Composition step` - This step will run a composition which use your chat image from the build step, docker image of curl and check if your application is responsive. It will do so by printing "works" if a curl command to our app at port 5000 succeed.

In the root of this repository you'll find a file named codefresh.yml, this is our build descriptor and it describes the different steps that comprise our process. Let's quickly review the contents of this file: