Update examples

Signed-off-by: Constantin Muraru <[email protected]>

Author: Constantin Muraru

README.md

@@ -1,8 +1,27 @@
 # himl
-A hierarchical config using yaml in Python
+A hierarchical config using yaml in Python.
 
 Latest version is: 0.1.17
 
+## Description
+
+A python module which allows you to merge hierarchical config files using YAML syntax. It offers deep merge, variable interpolation and secrets retrieval from secrets managers.
+
+It is ideal if you want to structure your hierarchy in such a way that you avoid duplication. You can define a structure for your configuration using a hierarchy such environment/project/cluster/app. It is up to you what layers you want to use in this hierarchy. The tool will read all yaml files starting from the root (where default values would be) all the way to the leaf (where most specific values would be, which will take precedence).
+
+Idea came from puppet's hiera.
+
+## Table of Contents  
+
+1. [Installation](#installation)
+2. [Examples](#examples)
+3. [Features](#features)
+    * [Interpolation](#feature-interpolation)
+    * [Deep merge](#feature-deep-merge)
+    * [Secrets retrieval](#feature-secrets-retrieval)
+    * [Merge with Terraform remote state](#feature-terraform-remote-state)
+
+<a name="installation"/>
 
 ## Installation
 
@@ -20,10 +39,80 @@ cd himl
 sudo python setup.py install
 ```
 
-## Example
+<a name="examples"/>
+
+## Examples
+
+### Using the python module
+
+This will merge simple/default.yaml with simple/production/env.yaml
+```py
+from himl import ConfigProcessor
+
+config_processor = ConfigProcessor()
+path = "examples/simple/production"
+filters = () # can choose to output only specific keys
+exclude_keys = () # can choose to remove specific keys
+output_format = "yaml" # yaml/json
+
+
+config_processor.process(path=path, filters=filters, exclude_keys=exclude_keys, 
+                         output_format=output_format, print_data=True)
+
+```
+
+The above example will merge `simple/default.yaml` with `simple/production/env.yaml`:
+```
+$ tree examples/simple
+examples/simple
+├── default.yaml
+└── production
+    └── env.yaml
+```
+
+<a name="deep-merge-example"/>
+
+The example also showcases deep merging of lists and maps.
+
+`examples/simple/default.yaml`
+```yaml
+---
+env: default
+deep:
+  key1: v1
+  key2: v2
+deep_list:
+  - item1
+  - item2
+```
+
+`examples/simple/production/env.yaml`
+```yaml
+---
+env: prod
+deep:
+  key3: v3
+deep_list:
+  - item3
+```
+
+Result:
+```yaml
+env: prod
+deep:
+  key1: v1
+  key2: v2
+  key3: v3
+deep_list:
+- item1
+- item2
+- item3
+```
 
 ### Using the cli
 
+A cli tool called `himl` is automatically installed via `pip`. You can use it to parse a tree of yamls and it will either output the combined configuration at standard output or write it to a file.
+
 ```sh
 usage: himl [-h] [--output-file OUTPUT_FILE] [--format OUTPUT_FORMAT]
              [--filter FILTER] [--exclude EXCLUDE]
@@ -34,10 +123,10 @@ usage: himl [-h] [--output-file OUTPUT_FILE] [--format OUTPUT_FORMAT]
 ```
 
 ```sh
-himl examples/config_example/env=dev/region=us-east-1/cluster=cluster2
+himl examples/complex/env=dev/region=us-east-1/cluster=cluster2
 ```
 
-The configuration output will be something like this:
+Based on the configuration tree from the [examples/complex](examples/complex) folder, the output of the above command will be the following:
 ```
 cluster:
   description: 'This is cluster: cluster2. It is using c3.2xlarge instance type.'
@@ -50,8 +139,8 @@ env: dev
 
 Where the examples folder looks something like this:
 ```
-$ tree examples/config_example
-examples/config_example
+$ tree examples/complex
+examples/complex
 ├── default.yaml
 ├── env=dev
 │   ├── env.yaml
@@ -73,18 +162,87 @@ examples/config_example
         └── region.yaml
 ```
 
-### Using the python module
+<a name="features"/>
 
-```py
-from himl import ConfigProcessor
+## Features
 
-config_processor = ConfigProcessor()
-path = "examples/config_example/env=dev/region=us-east-1/cluster=cluster2"
-filters = () # can choose to output only specific keys
-exclude_keys = () # can choose to remove specific keys
-output_format = "yaml" # yaml/json
+<a name="feature-interpolation"/>
 
+### Interpolation
 
-config_processor.process(path=path, filters=filters, exclude_keys=exclude_keys, 
-                         output_format=output_format, print_data=True)
+In order to avoid repetition, we wanted to make it possible to define a value once and reuse it in other parts of the yaml config.
+Unlike yaml anchors, these interpolations work across multiple files.
+
+#### Interpolating simple values
+
+`data/default.yaml`:
+```yaml
+allowed_roles:
+  - "arn:aws:iam::{{account.id}}:role/myrole"
+```
+
+`data/dev/env.yaml`:
+```
+account:
+  id: "123456"
+```
+
+#### Interpolating whole `dict`
+
+```yaml
+projects:
+  webapp1:
+    tagging:
+      Owner: "Web Service Team"
+      Environment: "dev"
+      CostCenter: "123"
+  data-store:
+      Owner: "Backend Team"
+      Environment: "dev"
+      CostCenter: "455"
+
+# this will copy the whole projects.webapp1.tagging dict to this key
+tagging: "{{projects.webapp1.tagging}}"
+
+# or even a double interpolation
+tagging: "{{projects.{{project.name}}.tagging}}"
+```
+
+<a name="feature-deep-merge"/>
+
+### Deep merge
+
+It's possible to have the same key (eg. a dict/list) in multiple files and combine them using a deep merge.
+See an example [here](https://github.com/adobe/himl#deep-merge-example).
+
+<a name="feature-secrets-retrieval"/>
+
+### Secrets retrieval
+
+#### [AWS SSM](https://docs.aws.amazon.com/systems-manager/latest/userguide/integration-ps-secretsmanager.html)
+
+```yaml
+passphrase: "{{ssm.path(/key/coming/from/aws/secrets/store/manager).aws_profile(myprofile)}}"
 ```
+
+#### [Vault](https://www.vaultproject.io/)
+
+Not yet implemented.
+
+
+<a name="feature-terraform-remote-state"/>
+
+### Merge with [Terraform remote state](https://www.terraform.io/docs/state/remote.html)
+
+```yaml
+### Terraform remote states ###
+remote_states:
+  - name: cluster_composition
+    type: terraform
+    aws_profile: "my_aws_profile"
+    s3_bucket: "my_terraform_bucket"
+    s3_key: "mycluster.tfstate"
+
+
+endpoint: "{{outputs.cluster_composition.output.value.redis_endpoint}}"
+```