How to Merge Helm Chart Values Per Environment in Python

Merge default Helm chart values with environment-specific overrides using a recursive dictionary merge function, then write each environment's YAML file.

Easy Python 3.9+ Aug 9, 2026 Production deployment patterns 11 views 0 copies

helm merge yaml deployment configuration

Python code

41 lines

Python 3.9+

from pathlib import Path
import json
import tempfile


DEFAULT_VALUES = {
    "image": "nginx:latest",
    "replicas": 1,
    "resources": {"cpu": "100m", "memory": "128Mi"},
}

ENV_OVERRIDES = {
    "dev": {"replicas": 1, "resources": {"cpu": "50m"}},
    "staging": {"replicas": 2, "resources": {"cpu": "250m", "memory": "256Mi"}},
    "prod": {"replicas": 4, "resources": {"cpu": "500m", "memory": "1Gi"}, "image": "nginx:1.21.6"},
}


def merge_values(base: dict, override: dict) -> dict:
    result = base.copy()
    for key, value in override.items():
        if isinstance(value, dict) and isinstance(result.get(key), dict):
            result[key] = merge_values(result[key], value)
        else:
            result[key] = value
    return result


def generate_chart_values(env: str) -> dict:
    if env not in ENV_OVERRIDES:
        raise ValueError(f"Unknown environment: {env}")
    return merge_values(DEFAULT_VALUES, ENV_OVERRIDES[env])


if __name__ == "__main__":
    with tempfile.TemporaryDirectory() as tmpdir:
        for env in ["dev", "staging", "prod"]:
            values = generate_chart_values(env)
            out_path = Path(tmpdir) / f"values-{env}.yaml"
            out_path.write_text(json.dumps(values, indent=2))
            print(f"{env}: {out_path} -> {json.dumps(values)}")

Output

stdout

dev: /tmp/tmp123456/values-dev.yaml -> {"image": "nginx:latest", "replicas": 1, "resources": {"cpu": "50m", "memory": "128Mi"}}
staging: /tmp/tmp123456/values-staging.yaml -> {"image": "nginx:latest", "replicas": 2, "resources": {"cpu": "250m", "memory": "256Mi"}}
prod: /tmp/tmp123456/values-prod.yaml -> {"image": "nginx:1.21.6", "replicas": 4, "resources": {"cpu": "500m", "memory": "1Gi"}}

How it works

The merge_values function recursively merges two dictionaries: if both the base and override have a dict for the same key, it merges them recursively rather than replacing the entire dict. This allows partial overrides like updating only the CPU in the resources dict while keeping the memory value from the defaults. The generate_chart_values function validates the environment name and then applies the override to the defaults. The script writes each environment's merged values as a JSON file (a stand-in for YAML in this example) inside a temporary directory, which is useful for generating Helm values files during deployment.

Common mistakes

Using a shallow copy or .update() for nested dicts, which replaces the whole resources dict instead of merging nested keys.
Forgetting to validate the environment name, leading to silent default values instead of an error.
Writing YAML as plain text without proper quoting or formatting, which can break Helm parsing.
Hardcoding file paths instead of using tempfile or a configured output directory.

Variations

Use PyYAML to actually write YAML files instead of JSON by adding yaml.safe_dump(values).
Load overrides from separate YAML files per environment instead of a hardcoded dict.

Real-world use cases

CI/CD pipelines that generate per-environment Helm values files before deploying to dev, staging, and prod clusters.
Multi-tenant SaaS deployments where each customer or region requires different resource limits and image versions.
Infrastructure-as-code scripts that need to merge cloud-provider-specific settings with common service defaults.

How to Merge Helm Chart Values Per Environment in Python

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

More from Production deployment patterns

Tutorials

Quizzes

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

More from Production deployment patterns

Keep learning

Tutorials

Quizzes