feat: add parameter utility

README.md

@@ -13,6 +13,7 @@ A suite of utilities for AWS Lambda Functions that makes tracing with AWS X-Ray,
 * **[Logging](https://awslabs.github.io/aws-lambda-powertools-python/core/logger/)** - Structured logging made easier, and decorator to enrich structured logging with key Lambda context details
 * **[Metrics](https://awslabs.github.io/aws-lambda-powertools-python/core/metrics/)** - Custom Metrics created asynchronously via CloudWatch Embedded Metric Format (EMF)
 * **[Bring your own middleware](https://awslabs.github.io/aws-lambda-powertools-python/utilities/middleware_factory/)** - Decorator factory to create your own middleware to run logic before, and after each Lambda invocation
+* **[Parameters utility](https://awslabs.github.io/aws-lambda-powertools-python/utilities/parameters/)** - Retrieve and cache parameter values
 
 ### Installation
 

aws_lambda_powertools/utilities/__init__.py

@@ -0,0 +1,3 @@
+# -*- coding: utf-8 -*-
+
+"""General utilities for Powertools"""

aws_lambda_powertools/utilities/parameters/__init__.py

@@ -0,0 +1,23 @@
+# -*- coding: utf-8 -*-
+
+"""
+Parameter retrieval and caching utility
+"""
+
+from .base import BaseProvider
+from .dynamodb import DynamoDBProvider
+from .exceptions import GetParameterError, TransformParameterError
+from .secrets import SecretsProvider, get_secret
+from .ssm import SSMProvider, get_parameter, get_parameters
+
+__all__ = [
+    "BaseProvider",
+    "GetParameterError",
+    "DynamoDBProvider",
+    "SecretsProvider",
+    "SSMProvider",
+    "TransformParameterError",
+    "get_parameter",
+    "get_parameters",
+    "get_secret",
+]

aws_lambda_powertools/utilities/parameters/base.py

@@ -0,0 +1,190 @@
+"""
+Base for Parameter providers
+"""
+
+import base64
+import json
+from abc import ABC, abstractmethod
+from collections import namedtuple
+from datetime import datetime, timedelta
+from typing import Dict, Optional, Union
+
+from .exceptions import GetParameterError, TransformParameterError
+
+DEFAULT_MAX_AGE_SECS = 5
+ExpirableValue = namedtuple("ExpirableValue", ["value", "ttl"])
+# These providers will be dynamically initialized on first use of the helper functions
+DEFAULT_PROVIDERS = {}
+
+
+class BaseProvider(ABC):
+    """
+    Abstract Base Class for Parameter providers
+    """
+
+    store = None
+
+    def __init__(self):
+        """
+        Initialize the base provider
+        """
+
+        self.store = {}
+
+    def get(
+        self, name: str, max_age: int = DEFAULT_MAX_AGE_SECS, transform: Optional[str] = None, **sdk_options
+    ) -> Union[str, list, dict, bytes]:
+        """
+        Retrieve a parameter value or return the cached value
+
+        Parameters
+        ----------
+        name: str
+            Parameter name
+        max_age: int
+            Maximum age of the cached value
+        transform: str
+            Optional transformation of the parameter value. Supported values
+            are "json" for JSON strings and "binary" for base 64 encoded
+            values.
+        sdk_options: dict, optional
+            Arguments that will be passed directly to the underlying API call
+
+        Raises
+        ------
+        GetParameterError
+            When the parameter provider fails to retrieve a parameter value for
+            a given name.
+        TransformParameterError
+            When the parameter provider fails to transform a parameter value.
+        """
+
+        # If there are multiple calls to the same parameter but in a different
+        # transform, they will be stored multiple times. This allows us to
+        # optimize by transforming the data only once per retrieval, thus there
+        # is no need to transform cached values multiple times. However, this
+        # means that we need to make multiple calls to the underlying parameter
+        # store if we need to return it in different transforms. Since the number
+        # of supported transform is small and the probability that a given
+        # parameter will always be used in a specific transform, this should be
+        # an acceptable tradeoff.
+        key = (name, transform)
+
+        if key not in self.store or self.store[key].ttl < datetime.now():
+            try:
+                value = self._get(name, **sdk_options)
+            # Encapsulate all errors into a generic GetParameterError
+            except Exception as exc:
+                raise GetParameterError(str(exc))
+
+            if transform is not None:
+                value = transform_value(value, transform)
+
+            self.store[key] = ExpirableValue(value, datetime.now() + timedelta(seconds=max_age),)
+
+        return self.store[key].value
+
+    @abstractmethod
+    def _get(self, name: str, **sdk_options) -> str:
+        """
+        Retrieve paramater value from the underlying parameter store
+        """
+        raise NotImplementedError()
+
+    def get_multiple(
+        self,
+        path: str,
+        max_age: int = DEFAULT_MAX_AGE_SECS,
+        transform: Optional[str] = None,
+        raise_on_transform_error: bool = False,
+        **sdk_options,
+    ) -> Union[Dict[str, str], Dict[str, dict], Dict[str, bytes]]:
+        """
+        Retrieve multiple parameters based on a path prefix
+
+        Parameters
+        ----------
+        path: str
+            Parameter path used to retrieve multiple parameters
+        max_age: int, optional
+            Maximum age of the cached value
+        transform: str, optional
+            Optional transformation of the parameter value. Supported values
+            are "json" for JSON strings and "binary" for base 64 encoded
+            values.
+        raise_on_transform_error: bool, optional
+            Raises an exception if any transform fails, otherwise this will
+            return a None value for each transform that failed
+        sdk_options: dict, optional
+            Arguments that will be passed directly to the underlying API call
+
+        Raises
+        ------
+        GetParameterError
+            When the parameter provider fails to retrieve parameter values for
+            a given path.
+        TransformParameterError
+            When the parameter provider fails to transform a parameter value.
+        """
+
+        key = (path, transform)
+
+        if key not in self.store or self.store[key].ttl < datetime.now():
+            try:
+                values = self._get_multiple(path, **sdk_options)
+            # Encapsulate all errors into a generic GetParameterError
+            except Exception as exc:
+                raise GetParameterError(str(exc))
+
+            if transform is not None:
+                new_values = {}
+                for key, value in values.items():
+                    try:
+                        new_values[key] = transform_value(value, transform)
+                    except Exception as exc:
+                        if raise_on_transform_error:
+                            raise exc
+                        else:
+                            new_values[key] = None
+
+                values = new_values
+
+            self.store[key] = ExpirableValue(values, datetime.now() + timedelta(seconds=max_age),)
+
+        return self.store[key].value
+
+    @abstractmethod
+    def _get_multiple(self, path: str, **sdk_options) -> Dict[str, str]:
+        """
+        Retrieve multiple parameter values from the underlying parameter store
+        """
+        raise NotImplementedError()
+
+
+def transform_value(value: str, transform: str) -> Union[dict, bytes]:
+    """
+    Apply a transform to a value
+
+    Parameters
+    ---------
+    value: str
+        Parameter alue to transform
+    transform: str
+        Type of transform, supported values are "json" and "binary"
+
+    Raises
+    ------
+    TransformParameterError:
+        When the parameter value could not be transformed
+    """
+
+    try:
+        if transform == "json":
+            return json.loads(value)
+        elif transform == "binary":
+            return base64.b64decode(value)
+        else:
+            raise ValueError(f"Invalid transform type '{transform}'")
+
+    except Exception as exc:
+        raise TransformParameterError(str(exc))