feat: Add .env file support for local Lambda invocations

requirements/base.txt

@@ -6,6 +6,7 @@ jmespath~=1.0.1
 ruamel_yaml~=0.18.15
 PyYAML~=6.0
 cookiecutter~=2.6.0
+python-dotenv~=1.0.0
 aws-sam-translator==1.101.0
 #docker minor version updates can include breaking changes. Auto update micro version only.
 docker~=7.1.0

requirements/reproducible-linux.txt

@@ -4,6 +4,9 @@
 #
 #    pip-compile --allow-unsafe --generate-hashes --output-file=requirements/reproducible-linux.txt
 #
+--extra-index-url https://plugin.us-east-1.prod.workshops.aws
+--trusted-host plugin.us-east-1.prod.workshops.aws
+
 annotated-types==0.7.0 \
     --hash=sha256:1f02e8b43a8fbbc3f3e0d4f0f4bfc8131bcb4eebe8849b8e5c773f3a1c582a53 \
     --hash=sha256:aff07c09a53a08bc8cfccb9c85b05f1aa9a2a6f23728d790723543408344ce89
@@ -661,6 +664,10 @@ python-dateutil==2.9.0.post0 \
     #   arrow
     #   botocore
     #   dateparser
+python-dotenv==1.0.1 \
+    --hash=sha256:e324ee90a023d808f1959c46bcbc04446a10ced277783dc6ee09987c37ec10ca \
+    --hash=sha256:f7b63ef50f1b690dddf550d03497b66d609393b40b564ed0d674909a68ebf16a
+    # via aws-sam-cli (setup.py)
 python-slugify==8.0.4 \
     --hash=sha256:276540b79961052b66b7d116620b36518847f52d5fd9e3a70164fc8c50faa6b8 \
     --hash=sha256:59202371d1d05b54a9e7720c5e038f928f45daaffe41dd10822f3907b937c856

requirements/reproducible-mac.txt

@@ -4,6 +4,9 @@
 #
 #    pip-compile --allow-unsafe --generate-hashes --output-file=requirements/reproducible-mac.txt
 #
+--extra-index-url https://plugin.us-east-1.prod.workshops.aws
+--trusted-host plugin.us-east-1.prod.workshops.aws
+
 annotated-types==0.7.0 \
     --hash=sha256:1f02e8b43a8fbbc3f3e0d4f0f4bfc8131bcb4eebe8849b8e5c773f3a1c582a53 \
     --hash=sha256:aff07c09a53a08bc8cfccb9c85b05f1aa9a2a6f23728d790723543408344ce89
@@ -661,6 +664,10 @@ python-dateutil==2.9.0.post0 \
     #   arrow
     #   botocore
     #   dateparser
+python-dotenv==1.0.1 \
+    --hash=sha256:e324ee90a023d808f1959c46bcbc04446a10ced277783dc6ee09987c37ec10ca \
+    --hash=sha256:f7b63ef50f1b690dddf550d03497b66d609393b40b564ed0d674909a68ebf16a
+    # via aws-sam-cli (setup.py)
 python-slugify==8.0.4 \
     --hash=sha256:276540b79961052b66b7d116620b36518847f52d5fd9e3a70164fc8c50faa6b8 \
     --hash=sha256:59202371d1d05b54a9e7720c5e038f928f45daaffe41dd10822f3907b937c856

samcli/commands/local/cli_common/invoke_context.py

@@ -10,6 +10,8 @@
 from pathlib import Path
 from typing import Any, Dict, List, Optional, TextIO, Tuple, Type, cast
 
+from dotenv import dotenv_values
+
 from samcli.commands._utils.template import TemplateFailedParsingException, TemplateNotFoundException
 from samcli.commands.exceptions import ContainersInitializationException
 from samcli.commands.local.cli_common.user_exceptions import DebugContextException, InvokeContextException
@@ -76,6 +78,7 @@ def __init__(
         template_file: str,
         function_identifier: Optional[str] = None,
         env_vars_file: Optional[str] = None,
+        dotenv_file: Optional[str] = None,
         docker_volume_basedir: Optional[str] = None,
         docker_network: Optional[str] = None,
         log_file: Optional[str] = None,
@@ -84,6 +87,7 @@ def __init__(
         debug_args: Optional[str] = None,
         debugger_path: Optional[str] = None,
         container_env_vars_file: Optional[str] = None,
+        container_dotenv_file: Optional[str] = None,
         parameter_overrides: Optional[Dict] = None,
         layer_cache_basedir: Optional[str] = None,
         force_image_build: Optional[bool] = None,
@@ -110,6 +114,8 @@ def __init__(
             Identifier of the function to invoke
         env_vars_file str
             Path to a file containing values for environment variables
+        dotenv_file str
+            Path to .env file containing environment variables
         docker_volume_basedir str
             Directory for the Docker volume
         docker_network str
@@ -126,6 +132,10 @@ def __init__(
             Additional arguments passed to the debugger
         debugger_path str
             Path to the directory of the debugger to mount on Docker
+        container_env_vars_file str
+            Path to a file containing values for container environment variables
+        container_dotenv_file str
+            Path to .env file containing container environment variables
         parameter_overrides dict
             Values for the template parameters
         layer_cache_basedir str
@@ -159,6 +169,7 @@ def __init__(
         self._template_file = template_file
         self._function_identifier = function_identifier
         self._env_vars_file = env_vars_file
+        self._dotenv_file = dotenv_file
         self._docker_volume_basedir = docker_volume_basedir
         self._docker_network = docker_network
         self._log_file = log_file
@@ -167,6 +178,7 @@ def __init__(
         self._debug_args = debug_args
         self._debugger_path = debugger_path
         self._container_env_vars_file = container_env_vars_file
+        self._container_dotenv_file = container_dotenv_file
 
         self._parameter_overrides = parameter_overrides
         # Override certain CloudFormation pseudo-parameters based on values provided by customer
@@ -245,8 +257,25 @@ def __enter__(self) -> "InvokeContext":
             *_function_providers_args[self._containers_mode]
         )
 
-        self._env_vars_value = self._get_env_vars_value(self._env_vars_file)
-        self._container_env_vars_value = self._get_env_vars_value(self._container_env_vars_file)
+        # Load and merge Lambda runtime environment variables
+        # Dotenv values are loaded first with function-specific parsing enabled
+        # Then JSON env_vars can override them
+        # Lambda env vars support hierarchical structure with Parameters and function-specific sections
+        dotenv_vars = self._get_dotenv_values(self._dotenv_file, parse_function_specific=True)
+        env_vars = self._get_env_vars_value(self._env_vars_file)
+        self._env_vars_value = self._merge_env_vars(dotenv_vars, env_vars, wrap_in_parameters=True)
+
+        # Load and merge container environment variables (used for debugging)
+        # Container env vars remain flat (not wrapped in Parameters, no function-specific parsing)
+        container_dotenv_vars = self._get_dotenv_values(self._container_dotenv_file, parse_function_specific=False)
+        container_env_vars = self._get_env_vars_value(self._container_env_vars_file)
+        self._container_env_vars_value = self._merge_env_vars(
+            container_dotenv_vars, container_env_vars, wrap_in_parameters=False
+        )
+
+        LOG.debug("Final env vars value: %s", self._env_vars_value)
+        LOG.debug("Final container env vars value: %s", self._container_env_vars_value)
+
         self._log_file_handle = self._setup_log_file(self._log_file)
 
         # in case of warm containers && debugging is enabled && if debug-function property is not provided, so
@@ -623,6 +652,172 @@ def _get_stacks(self) -> List[Stack]:
             LOG.debug("Can't read stacks information, either template is not found or it is invalid", exc_info=ex)
             raise ex
 
+    @staticmethod
+    def _merge_env_vars(
+        dotenv_vars: Optional[Dict], json_env_vars: Optional[Dict], wrap_in_parameters: bool
+    ) -> Optional[Dict]:
+        """
+        Merge environment variables from .env file and JSON file, with JSON taking precedence.
+
+        When wrap_in_parameters=True (Lambda env vars):
+        - dotenv_vars may already have hierarchical structure: {"Parameters": {...}, "FunctionName": {...}}
+        - If dotenv_vars is flat, wrap it in Parameters
+        - json_env_vars merges with Parameters section and preserves function-specific sections
+
+        When wrap_in_parameters=False (container env vars):
+        - Both dotenv_vars and json_env_vars should be flat
+        - Simple key-value merge with JSON taking precedence
+
+        :param dict dotenv_vars: Variables loaded from .env file (may be hierarchical or flat)
+        :param dict json_env_vars: Variables loaded from JSON file
+        :param bool wrap_in_parameters: If True, ensure hierarchical structure for Lambda env vars
+        :return dict: Merged environment variables, or None if both inputs are None
+        """
+        # Handle mocked test scenarios where json_env_vars might not be a dict
+        # This check must come before other logic to handle Mock objects properly
+        if json_env_vars is not None and not isinstance(json_env_vars, dict):
+            return json_env_vars  # type: ignore[return-value, unreachable]
+
+        # If both inputs are empty, return None early
+        if not dotenv_vars and not json_env_vars:
+            return None
+
+        # Initialize result based on dotenv_vars structure
+        if not dotenv_vars:
+            result = {}
+        elif wrap_in_parameters:
+            # Check if dotenv_vars is already hierarchical (has Parameters key)
+            if "Parameters" in dotenv_vars:
+                # Already hierarchical from parse_function_specific=True
+                result = {k: v.copy() if isinstance(v, dict) else v for k, v in dotenv_vars.items()}
+            else:
+                # Flat structure, wrap in Parameters
+                result = {"Parameters": dotenv_vars.copy()}
+        else:
+            # Container mode: keep flat
+            result = dotenv_vars.copy()
+
+        # Merge JSON env vars with precedence
+        if json_env_vars:
+            if wrap_in_parameters:
+                # Lambda env vars mode: handle hierarchical structure
+                if "Parameters" in json_env_vars:
+                    # Merge Parameters sections, with json_env_vars taking precedence
+                    if "Parameters" not in result:
+                        result["Parameters"] = {}
+                    result["Parameters"] = {**result.get("Parameters", {}), **json_env_vars["Parameters"]}
+
+                # Merge function-specific sections and other keys
+                for key, value in json_env_vars.items():
+                    if key != "Parameters":
+                        if key in result and isinstance(result[key], dict) and isinstance(value, dict):
+                            # Merge function-specific dicts, JSON takes precedence
+                            result[key] = {**result[key], **value}
+                        else:
+                            # Simple override
+                            result[key] = value
+            else:
+                # Container env vars mode: simple flat merge
+                result.update(json_env_vars)
+
+        return result if result else None
+
+    @staticmethod
+    def _get_dotenv_values(filename: Optional[str], parse_function_specific: bool = False) -> Optional[Dict]:
+        """
+        If the user provided a .env file, this method will read the file and return its values as a dictionary.
+        Optionally parses function-specific environment variables using FunctionName_VAR pattern.
+
+        :param string filename: Path to .env file containing environment variable values
+        :param bool parse_function_specific: If True, parse variables with FunctionName_VAR pattern into
+                                            function-specific sections. If False, returns flat dictionary.
+        :return dict: Value of environment variables from .env file, if provided. None otherwise
+                     When parse_function_specific=True, returns hierarchical structure:
+                     {"Parameters": {...global vars...}, "FunctionName": {...function vars...}}
+        :raises InvokeContextException: If the file was not found or could not be parsed
+        """
+        if not filename:
+            return None
+
+        # Check if file exists before attempting to read
+        if not os.path.exists(filename):
+            raise InvalidEnvironmentVariablesFileException("Environment variables file not found: {}".format(filename))
+
+        try:
+            # dotenv_values returns a dictionary with all variables from the .env file
+            # It handles comments, quotes, multiline values, etc.
+            env_dict = dotenv_values(filename)
+
+            # Log warning if file is empty or couldn't be parsed
+            if not env_dict:
+                LOG.warning("The .env file '%s' is empty or contains no valid environment variables", filename)
+
+            # Filter out None values and convert to strings
+            clean_dict = {k: str(v) if v is not None else "" for k, v in env_dict.items()}
+
+            # If not parsing function-specific vars, return flat structure
+            if not parse_function_specific:
+                return clean_dict
+
+            # Parse function-specific variables
+            return InvokeContext._parse_function_specific_env_vars(clean_dict)
+
+        except Exception as ex:
+            raise InvalidEnvironmentVariablesFileException(
+                "Could not read environment variables from .env file {}: {}".format(filename, str(ex))
+            ) from ex
+
+    @staticmethod
+    def _parse_function_specific_env_vars(env_dict: Dict[str, str]) -> Dict:
+        """
+        Parse environment variables to separate global from function-specific variables.
+
+        Variables are classified as function-specific if they match the pattern: FunctionName_VAR
+        where FunctionName starts with an uppercase letter (PascalCase).
+
+        Examples:
+            MyFunction_API_KEY -> Function-specific for MyFunction
+            HelloWorld_TIMEOUT -> Function-specific for HelloWorld
+            LAMBDA_VAR -> Global (all uppercase, not PascalCase)
+            API_KEY -> Global (no underscore)
+            database_url -> Global (starts with lowercase)
+
+        :param dict env_dict: Flat dictionary of environment variables
+        :return dict: Hierarchical structure with Parameters and function-specific sections
+        """
+        result: Dict[str, Dict[str, str]] = {"Parameters": {}}
+
+        for key, value in env_dict.items():
+            # Check if variable contains underscore
+            if "_" not in key:
+                # No underscore -> global variable
+                result["Parameters"][key] = value
+                continue
+
+            # Split by first underscore to get function name prefix and variable name
+            parts = key.split("_", 1)
+            if len(parts) < 2:  # noqa: PLR2004
+                # Edge case: variable has underscore but split failed somehow
+                result["Parameters"][key] = value
+                continue
+
+            prefix, var_name = parts
+
+            # Check if prefix is PascalCase (starts with uppercase, not all uppercase)
+            # PascalCase: First char is uppercase AND not all chars are uppercase
+            is_pascal_case = prefix[0].isupper() and not prefix.isupper()
+
+            if is_pascal_case:
+                # Function-specific variable: FunctionName_VAR
+                if prefix not in result:
+                    result[prefix] = {}
+                result[prefix][var_name] = value
+            else:
+                # Global variable (ALL_CAPS, snake_case, etc.)
+                result["Parameters"][key] = value
+
+        return result
+
     @staticmethod
     def _get_env_vars_value(filename: Optional[str]) -> Optional[Dict]:
         """

samcli/commands/local/cli_common/options.py

@@ -174,6 +174,14 @@ def invoke_common_options(f):
                 type=click.Path(exists=True),
                 help="JSON file containing values for Lambda function's environment variables.",
             ),
+            click.option(
+                "--dotenv",
+                type=click.Path(exists=True),
+                help="Path to a .env file containing environment variables for Lambda functions. "
+                "Variables defined here will apply to all functions. "
+                "If both --env-vars and --dotenv are provided, variables from both will be merged "
+                "with --env-vars taking precedence.",
+            ),
             parameter_override_click_option(),
             click.option(
                 "--debug-port",
@@ -196,6 +204,14 @@ def invoke_common_options(f):
                 help="JSON file containing additional environment variables to be set within the container when "
                 "used in a debugging session locally.",
             ),
+            click.option(
+                "--container-dotenv",
+                type=click.Path(exists=True),
+                help="Path to a .env file containing additional environment variables to be set within the container "
+                "when used in a debugging session locally. "
+                "If both --container-env-vars and --container-dotenv are provided, variables from both will be merged "
+                "with --container-env-vars taking precedence.",
+            ),
             click.option(
                 "--docker-volume-basedir",
                 "-v",

samcli/commands/local/invoke/cli.py

@@ -92,10 +92,12 @@ def cli(
     event,
     no_event,
     env_vars,
+    dotenv,
     debug_port,
     debug_args,
     debugger_path,
     container_env_vars,
+    container_dotenv,
     docker_volume_basedir,
     docker_network,
     log_file,
@@ -130,10 +132,12 @@ def cli(
         event,
         no_event,
         env_vars,
+        dotenv,
         debug_port,
         debug_args,
         debugger_path,
         container_env_vars,
+        container_dotenv,
         docker_volume_basedir,
         docker_network,
         log_file,
@@ -160,10 +164,12 @@ def do_cli(  # pylint: disable=R0914
     event,
     no_event,
     env_vars,
+    dotenv,
     debug_port,
     debug_args,
     debugger_path,
     container_env_vars,
+    container_dotenv,
     docker_volume_basedir,
     docker_network,
     log_file,
@@ -211,6 +217,7 @@ def do_cli(  # pylint: disable=R0914
             template_file=template,
             function_identifier=function_identifier,
             env_vars_file=env_vars,
+            dotenv_file=dotenv,
             docker_volume_basedir=docker_volume_basedir,
             docker_network=docker_network,
             log_file=log_file,
@@ -219,6 +226,7 @@ def do_cli(  # pylint: disable=R0914
             debug_args=debug_args,
             debugger_path=debugger_path,
             container_env_vars_file=container_env_vars,
+            container_dotenv_file=container_dotenv,
             parameter_overrides=parameter_overrides,
             layer_cache_basedir=layer_cache_basedir,
             force_image_build=force_image_build,