# The Helmfile Best Practices Guide

This guide covers the Helmfile’s considered patterns for writing advanced helmfiles. It focuses on how helmfile should be structured and executed.

## Layering

You may occasionally end up with many helmfiles that shares common parts like which repositories to use, and whichi release to be bundled by default.

Use Layering to extract te common parts into a dedicated *library helmfile*s, so that each helmfile becomes DRY.

Let's assume that your `helmfile.yaml` looks like:

```
{ readFile "commons.yaml" }}
---
{{ readFile "environments.yaml" }}
---
releases:
- name: myapp
  chart: mychart
```

Whereas `commons.yaml` contained a monitoring agent:

```yaml
releases:
- name: metricbaet
  chart: stable/metricbeat
```

And `environments.yaml` contained well-known environments:

```yaml
environments:
  development:
  production:
```

At run time, template expressions in your `helmfile.yaml` are executed:

```yaml
releases:
- name: metricbaet
  chart: stable/metricbeat
---
environments:
  development:
  production:
---
releases:
- name: myapp
  chart: mychart
```

Resulting YAML documents are merged in the order of occurrence,
so that your `helmfile.yaml` becomes:

```yaml
environments:
  development:
  production:

releases:
- name: metricbaet
  chart: stable/metricbeat
- name: myapp
  chart: mychart
```

Great!

Now, repeat the above steps for each your `helmfile.yaml`, so that all your helmfiles becomes DRY.