feat: Support HTTP in MCP by Anarion-zuo · Pull Request #6109 · feast-dev/feast

Anarion-zuo · 2026-03-15T13:07:52Z

What this PR does / why we need it:

This PR adds first-class support for Streamable HTTP MCP transport in the Feast Python Feature Server to address reliability issues with the legacy SSE-based MCP endpoint and eliminate the need for external proxies in common MCP clients.

Key changes:

Adds mcp_transport configuration for MCP feature server ( sse | http ), defaulting to sse for backwards compatibility.
When mcp_transport=http , mounts MCP using Streamable HTTP via FastApiMCP.mount_http() .
When mcp_transport=sse , preserves existing behavior, preferring mount_sse() when available (fallback to deprecated mount() for older fastapi_mcp versions).
Fails fast with a clear error when mcp_transport=http is configured but the installed fastapi_mcp version does not support mount_http() .
Adds/updates unit + integration tests covering transport selection and failure modes.
Updates docs and example configuration to show how to enable Streamable HTTP and avoid the GET /mcp 406 by using the correct Accept header.
Touched areas:
MCP config + mounting logic: mcp_config.py , mcp_server.py , feature_server.py
Tests: test_mcp_server.py , test_mcp_feature_server.py
Docs/examples: genai.md , mcp-feature-server.md , feature_store.yaml

Which issue(s) this PR fixes:

Fixes #5853.

Misc

Tests run locally:

pytest sdk/python/tests/unit/infra/feature_servers/test_mcp_server.py
pytest sdk/python/tests/integration/test_mcp_feature_server.py
Notes:
Default remains mcp_transport: sse to avoid behavior changes for existing deployments.
For Streamable HTTP, a plain GET /mcp may return 406 unless the client includes Accept: text/event-stream (expected by the transport).

Signed-off-by: aaronzuo <[email protected]>

devin-ai-integration

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 3 additional findings.

Signed-off-by: aaronzuo <[email protected]>

franciscojavierarceo · 2026-03-16T14:21:18Z

.github/workflows/unit_tests.yml

      - name: Minimize uv cache
        run: uv cache prune --ci

+  mcp-feature-server-runtime:


this should go in integration tests please

Is it this one? .github/workflows/pr_integration_tests.yml

franciscojavierarceo · 2026-03-16T14:22:15Z

sdk/python/feast/ui_server.py

    tls_key_path: str = "",
    tls_cert_path: str = "",
 ):
+    import uvicorn


why move this here?

No need to import this if start_server is not called. But this is not essential. Will move it to the top.

franciscojavierarceo

overall this lgtm with two minor nits, thanks for doing this!

Signed-off-by: aaronzuo <[email protected]>

Anarion-zuo · 2026-03-17T08:24:45Z

Resolved your comments. @franciscojavierarceo

Signed-off-by: aaronzuo <[email protected]>

Anarion-zuo · 2026-03-17T14:13:58Z

@franciscojavierarceo Perhaps we can merge this one?

franciscojavierarceo

this lgtm, let's wait for @YassinNouh21 to review

YassinNouh21 · 2026-03-17T15:17:47Z

sdk/python/feast/feature_server.py

+                )
+
+                mcp_transport_not_supported_error = McpTransportNotSupportedError
+            except Exception as e:


except Exception here catches SyntaxError, AttributeError, etc. — not just a missing package. Use except ImportError so real bugs in mcp_server.py are not silently swallowed. @franciscojavierarceo worth fixing before merge.

cc: @franciscojavierarceo

YassinNouh21 · 2026-03-17T15:17:59Z

sdk/python/feast/infra/mcp_servers/mcp_server.py

-        # Mount the MCP server to the FastAPI app
-        mcp.mount()
+        transport: Literal["sse", "http"] = (
+            getattr(config, "mcp_transport", "sse") or "sse"


or "sse" handles None but mcp_transport is now Literal["sse", "http"] so None is impossible. Can simplify to getattr(config, "mcp_transport", "sse").

YassinNouh21 · 2026-03-17T15:18:10Z

sdk/python/feast/infra/mcp_servers/mcp_server.py

+            if mount_sse is not None:
+                mount_sse()
+            else:
+                mcp.mount()


Silent fallback to the deprecated mount() with no warning. Operator configured mcp_transport: sse but gets legacy behavior with no indication. Worth a logger.warning here.

YassinNouh21 · 2026-03-17T15:18:23Z

sdk/python/feast/infra/mcp_servers/mcp_server.py

+            else:
+                mcp.mount()
+        else:
+            raise McpTransportNotSupportedError(


This branch is unreachable — Literal["sse", "http"] in the config rejects anything else at parse time. Either remove it or add a comment that it's a defensive guard for programmatic callers.

@Anarion-zuo u didn't solve it btw :)

YassinNouh21 · 2026-03-17T15:18:35Z

sdk/python/feast/infra/mcp_servers/mcp_server.py

+    except McpTransportNotSupportedError:
+        raise
    except Exception as e:
        logger.error(f"Failed to initialize MCP integration: {e}")


Missing exc_info=True — loses the traceback. Without it, debugging a broken init means guessing from just the exception message string.

YassinNouh21 · 2026-03-17T15:18:48Z

.github/workflows/pr_integration_tests.yml

+            -H "Content-Type: application/json" \
+            -H "mcp-protocol-version: 2025-03-26" \
+            --data '{}' \
+            http://127.0.0.1:6566/mcp || true


|| true swallows connection failures. If the server crashed or is unreachable, curl exits non-zero but the step continues and later grep on a missing/empty file gives a confusing error. Remove || true and let curl fail the step directly.

YassinNouh21 · 2026-03-17T15:19:00Z

.github/workflows/pr_integration_tests.yml

+          SERVER_PID=$!
+          echo $SERVER_PID > /tmp/feast_server_pid
+          for i in $(seq 1 60); do
+            if curl -fsS http://127.0.0.1:6566/health >/dev/null; then


If the server crashes immediately after backgrounding, this loop burns 60 seconds before failing. Add kill -0 "$SERVER_PID" || { echo "server died"; exit 1; } at the top of the loop body.

cc: @franciscojavierarceo

Signed-off-by: aaronzuo <[email protected]>

Anarion-zuo · 2026-03-17T15:45:50Z

Addressed all of the reviews. Waiting for CI to go green.

Signed-off-by: aaronzuo <[email protected]>

Anarion-zuo · 2026-03-18T03:41:11Z

@franciscojavierarceo @YassinNouh21 It's green now.

Anarion-zuo · 2026-03-21T06:21:07Z

@franciscojavierarceo @YassinNouh21 gentle ping

feat: Support HTTP in MCP

3c8e090

Signed-off-by: aaronzuo <[email protected]>

Anarion-zuo requested a review from a team as a code owner March 15, 2026 13:07

dev

91a5692

Signed-off-by: aaronzuo <[email protected]>

Anarion-zuo mentioned this pull request Mar 15, 2026

Support Streamable HTTP transport for Feature Server MCP integration #5853

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Anarion-zuo added 4 commits March 15, 2026 21:16

format

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fix

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franciscojavierarceo reviewed Mar 16, 2026

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Anarion-zuo force-pushed the aaronzuo/mcp_http_config branch from 3ee0133 to 36f1bdf Compare March 17, 2026 08:24

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fix

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Signed-off-by: aaronzuo <[email protected]>

franciscojavierarceo requested a review from YassinNouh21 March 17, 2026 14:25

franciscojavierarceo approved these changes Mar 17, 2026

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fix reviews

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Anarion-zuo force-pushed the aaronzuo/mcp_http_config branch from 7d4360c to 0c897c6 Compare March 17, 2026 15:38

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fix logger

76224aa

Signed-off-by: aaronzuo <[email protected]>

fix logger test

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Anarion-zuo commented Mar 15, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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What this PR does / why we need it:

Which issue(s) this PR fixes:

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