ecs-mcp-server: calculate_time_window crashes when start_time/end_time are passed as strings via MCP

[project0]

Describe the bug

When invoking the ecs_troubleshooting_tool via MCP with actions that accept start_time/end_time parameters (fetch_task_failures, fetch_service_events, fetch_task_logs), the call crashes with AttributeError: 'str' object has no attribute 'tzinfo'.

MCP tool parameters are JSON-encoded, so start_time and end_time always arrive as strings (e.g. "2026-04-03T10:00:00Z"). The transformers in ecs_troubleshooting.py pass these strings through to calculate_time_window(), which expects datetime objects.

Expected Behavior

String-valued start_time/end_time parameters should be parsed into datetime objects before being passed to calculate_time_window(), and the troubleshooting action should execute successfully.

Current Behavior

The call fails immediately with:

2026-04-03 11:58:36,184 - awslabs.ecs_mcp_server.api.troubleshooting_tools.fetch_task_failures - ERROR - Error in fetch_task_failures: 'str' object has no attribute 'tzinfo'
Traceback (most recent call last):
  File ".../awslabs/ecs_mcp_server/api/troubleshooting_tools/fetch_task_failures.py", line 218, in fetch_task_failures
    actual_start_time, actual_end_time = calculate_time_window(
        time_window, start_time, end_time
    )
  File ".../awslabs/ecs_mcp_server/utils/time_utils.py", line 54, in calculate_time_window
    end_time if end_time.tzinfo else end_time.replace(tzinfo=datetime.timezone.utc)
AttributeError: 'str' object has no attribute 'tzinfo'

Reproduction Steps

Call the ecs_troubleshooting_tool MCP tool with a string-valued end_time or start_time:

await ecs_troubleshooting_tool(
    action="fetch_task_failures",
    parameters={
        "ecs_cluster_name": "my-cluster",
        "time_window": 3600,
        "end_time": "2026-04-03T12:00:00Z",  # string, as MCP delivers it
    },
)

Possible Solution

Parse string inputs to datetime at the boundary in utils/time_utils.py:

from datetime import datetime, timezone

def _ensure_datetime(value):
    if value is None:
        return None
    if isinstance(value, str):
        return datetime.fromisoformat(value.replace("Z", "+00:00"))
    return value

def calculate_time_window(time_window=3600, start_time=None, end_time=None):
    start_time = _ensure_datetime(start_time)
    end_time = _ensure_datetime(end_time)
    # ... rest unchanged

Alternatively, the transformers in ecs_troubleshooting.py (lines 99-104, 130-134, 164-171) could parse the strings before forwarding.

Additional Information/Context

This affects any MCP client that invokes these actions with explicit time parameters. Since MCP uses JSON serialization, datetime values will always arrive as strings — there is no datetime type in JSON.

OS

Linux

Server

ecs-mcp-server

Server Version

No response

Region experiencing the issue

eu-central-1

Other information

The same bug pattern likely exists in fetch_service_events and fetch_task_logs since they use the same transformer pattern and call calculate_time_window the same way.

Service quota

• I have reviewed the service quotas for this construct