himl

A hierarchical config using yaml in Python.

Latest version is: 0.15.2

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

• himl
  • Description
  • Table of Contents
  • Installation
    • Using pip
    • Using docker image
    • From Source
  • Examples
    • Using the python module
    • Using the cli
  • Features
    • Interpolation
      • Interpolating simple values
      • Interpolating whole dict
    • Deep merge
    • Secrets retrieval
      • AWS SSM
      • AWS S3
      • Vault
    • Merge with Terraform remote state
    • Merge with env variables
  • himl config merger
    • Extra merger features

Installation

Using pip

pip install himl

Using docker image

docker run ghcr.io/adobe/himl:latest himl-config-merger --help

See all docker tags at: https://github.com/adobe/himl/pkgs/container/himl/versions

From Source

git clone https://github.com/adobe/himl
cd himl
sudo python install -e .

Examples

Using the python module

This will merge simple/default.yaml with simple/production/env.yaml

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

The example also showcases deep merging of lists and maps.

examples/simple/default.yaml

---
env: default
deep:
  key1: v1
  key2: v2
deep_list:
  - item1
  - item2

examples/simple/production/env.yaml

---
env: prod
deep:
  key3: v3
deep_list:
  - item3

Result:

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.

usage: himl [-h] [--output-file OUTPUT_FILE] [--format OUTPUT_FORMAT]
             [--filter FILTER] [--exclude EXCLUDE]
             [--skip-interpolation-validation]
             [--skip-interpolation-resolving] [--enclosing-key ENCLOSING_KEY]
             [--cwd CWD]
             [--list-merge-strategy {append,override,prepend,append_unique}]
             path

himl examples/complex/env=dev/region=us-east-1/cluster=cluster2

Based on the configuration tree from the 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.'
  name: cluster2
  node_type: c3.2xlarge
region:
  location: us-east-1
env: dev

Where the examples folder looks something like this:

$ tree examples/complex
examples/complex
├── default.yaml
├── env=dev
│   ├── env.yaml
│   ├── region=us-east-1
│   │   ├── cluster=cluster1
│   │   │   └── cluster.yaml
│   │   ├── cluster=cluster2
│   │   │   └── cluster.yaml
│   │   └── region.yaml
│   └── region=us-west-2
│       ├── cluster=cluster1
│       │   └── cluster.yaml
│       └── region.yaml
└── env=prod
    ├── env.yaml
    └── region=eu-west-2
        ├── cluster=ireland1
        │   └── cluster.yaml
        └── region.yaml

Features

Interpolation

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:

allowed_roles:
  - "arn:aws:iam::{{account.id}}:role/myrole"

data/dev/env.yaml:

account:
  id: "123456"

Interpolating whole dict

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}}"

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.

Secrets retrieval

AWS SSM

passphrase: "{{ssm.path(/key/coming/from/aws/secrets/store/manager).aws_profile(myprofile)}}"

AWS S3

my_value: "{{s3.bucket(my-bucket).path(path/to/file.txt).base64encode(true).aws_profile(myprofile)}}"

Vault

Use vault cli to authenticate, fallback method via LDAP.

Retrieve only one key value from a secret, the path tail is used as key:

my_value: "{{vault.key(/path/from/vault/key)}}"

Retrieve all key/value pairs from a vault path:

my_dict: "{{vault.path(/path/from/vault)}}"

Generate a token for a policy:

my_token: "{{vault.token_policy(my_vault_policy)}}"

Merge with Terraform remote state

### 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}}"

Merge with env variables

kubeconfig_location: "{{env(KUBECONFIG)}}"

himl-config-merger

The himl-config-merger script, contains logic of merging a hierarchical config directory and creating the end result YAML files.

himl-config-merger examples/complex --output-dir merged_output --levels env region cluster --leaf-directories cluster

INFO:__main__:Found input config directory: examples/complex/env=prod/region=eu-west-2/cluster=ireland1
INFO:__main__:Storing generated config to: merged_output/prod/eu-west-2/ireland1.yaml
INFO:__main__:Found input config directory: examples/complex/env=dev/region=us-west-2/cluster=cluster1
INFO:__main__:Storing generated config to: merged_output/dev/us-west-2/cluster1.yaml
INFO:__main__:Found input config directory: examples/complex/env=dev/region=us-east-1/cluster=cluster1
INFO:__main__:Storing generated config to: merged_output/dev/us-east-1/cluster1.yaml
INFO:__main__:Found input config directory: examples/complex/env=dev/region=us-east-1/cluster=cluster2
INFO:__main__:Storing generated config to: merged_output/dev/us-east-1/cluster2.yaml

Input example:

> tree examples/complex
examples/complex
├── default.yaml
├── env=dev
│   ├── env.yaml
│   ├── region=us-east-1
│   │   ├── cluster=cluster1
│   │   │   └── cluster.yaml
│   │   ├── cluster=cluster2
│   │   │   └── cluster.yaml
│   │   └── region.yaml
│   └── region=us-west-2
│       ├── cluster=cluster1
│       │   └── cluster.yaml
│       └── region.yaml
└── env=prod
    ├── env.yaml
    └── region=eu-west-2
        ├── cluster=ireland1
        │   └── cluster.yaml
        └── region.yaml

Output:

merged_output
├── dev
│   ├── us-east-1
│   │   ├── cluster1.yaml
│   │   └── cluster2.yaml
│   └── us-west-2
│       └── cluster1.yaml
└── prod
    └── eu-west-2
        └── ireland1.yaml

Leveraging HIML, the config-merger script loads the configs tree structure and deep-merges all keys from all YAML files found from a root path to an edge. For each leaf directory, a file will be created under --output-dir.

Under each level, there is a mandatory "level key" that is used by config-merger for computing the end result. This key should be present in one of the files under each level. (eg. env.yaml under env).

Output filtering

Some configs that are specified in the higher levels of the directory tree might not be needed in the end (leaf) result. For this reason, the config-merger script can apply a set of filter rules that are specified via the --filter-rules-key parameter. This property must be present in the config and contains rules for removing root level keys from the output. The filter is applied if the selector object matches a subset of the output keys and will keep the keys specified in the values list or the keys that match the regex pattern.

# intermediate config after hierarchical merge
env: dev
cluster: cluster1
region: us-east-1
key1: persisted
key2: dropped
keep_1: persisted
tags:
  cost_center: 123
_filters:
- selector:
    env: "dev"
  keys:
    values:
    - key1
    regex: "keep_.*"
- selector:
    cluster:
      regex: "cluster1"
  keys:
    values:
    - tags

Build the output with filtering:

himl-config-merger examples/filters --output-dir merged_output --levels env region cluster --leaf-directories cluster --filter-rules-key _filters

# output after filtering
env: dev
cluster: cluster1
region: us-east-1
key1: persisted
keep_1: persisted
tags:
  cost_center: 123

Filtering limitations

Rule selectors and keys filtering only works at the root level of the config. It is not possible to filter nested keys.

Extra merger features

Apart from the standard features found in the PyYaml library, the himl-config-merger component also implements a custom YAML tag called !include.

Example:

VA7:     !include configs/env=int/region=va7/kafka-brokers.yaml regionBrokers.VA7

This will replace the value after interpolation with the value of the regionBrokers.VA7 found under the configs/env=int/region=va7/kafka-brokers.yaml path.

Custom merge strategy

An optional parameter type_strategies can be passed into ConfigProcessor to define custom merging behavior. It could be custom functions that fit your needs. Your function should take the arguments of (config, path, base, nxt) and return the merged result.

Example:

from himl import ConfigProcessor

def strategy_merge_override(config, path, base, nxt):
    """merge list of dicts. if objects have same id, nxt replaces base."""
    """if remove flag is present in nxt item, remove base and not add nxt"""
    result = deepcopy(base)
    for nxto in nxt:
        for baseo in result:
            # if list is not a list of dicts, bail out and let the next strategy to execute
            if not isinstance(baseo,dict) or not isinstance(nxto,dict):
                return STRATEGY_END
            if 'id' in baseo and 'id' in nxto and baseo['id'] == nxto['id']:
                result.remove(baseo) #same id, remove previous item
        if 'remove' not in nxto:
            result.append(nxto)
    return result

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,
                         type_strategies= [(list, [strategy_merge_override,'append']), (dict, ["merge"])] ))