SnapStart with Minimal API .Net 10 issue

[mikemike396]

Describe the bug

Were trying to get SnapStart working with a .Net 10 .zip function thats running Minimal API project.

When we upload a new zip and create the new version we see the /warmup endpoint hit but no other logs of SnapStart working or failing. Additionally after about 10 minutes we're seeing a [INIT_START] cold start of around 6s.

We expected to see logs such as [restoreDuration] on requests.

Any thoughts on why this isn't working?

Function Details
Runtime: .NET 10 (C#/F#/PowerShell)
Architecture: arm64
Memory: 512MB
Ephemeral storage: 512MB
Timeout: 15s
Function URL: Auth type = None

Regression Issue

• Select this option if this issue appears to be a regression.

Expected Behavior

SnapStart should be picking up requests on cold starts.

Current Behavior

SnapStart is not reducing cold init starts.

Reproduction Steps

Program.cs

var builder = WebApplication.CreateBuilder(args);
var services = builder.Services;

// AWS Lambda hosting configuration
services.AddAWSLambdaHosting(LambdaEventSource.HttpApi);

// Add warm-up requests before snapshot
builder.Services.AddAWSLambdaBeforeSnapshotRequest(
    new HttpRequestMessage(HttpMethod.Get, "/warmup"));

app.MapGet("/warmup", () => "Warmup successful");

// Start the application
app.Run();

This is how we are publishing:
dotnet publish -c Release -r linux-arm64 --self-contained false -o ./lambda-publish

Possible Solution

No response

Additional Information/Context

When deploying a new version we see this:

2026-02-01T20:32:42.205Z
INIT_START Runtime Version: dotnet:10.v20 Runtime Version ARN: arn:aws:lambda:us-east-1::runtime:1b485095a08c766eafbff6b853f6e32d7a9fd64469bb1d0b1312a9e324113ea8
2026-02-01T20:32:43.438Z
warn: Amazon.Lambda.AspNetCoreServer.AbstractAspNetCoreFunction[0]
2026-02-01T20:32:43.438Z
Request does not contain domain name information but is derived from APIGatewayProxyFunction.
2026-02-01T20:32:43.465Z
info: Microsoft.AspNetCore.Hosting.Diagnostics[1]
2026-02-01T20:32:43.465Z
Request starting GET https:///warmup - - 0
2026-02-01T20:32:43.880Z
info: Microsoft.AspNetCore.Routing.EndpointMiddleware[0]
2026-02-01T20:32:43.880Z
Executing endpoint 'HTTP: GET /warmup'
2026-02-01T20:32:43.884Z
info: Microsoft.AspNetCore.Routing.EndpointMiddleware[1]
2026-02-01T20:32:43.884Z
Executed endpoint 'HTTP: GET /warmup'
2026-02-01T20:32:43.961Z
info: Microsoft.AspNetCore.Hosting.Diagnostics[2]
2026-02-01T20:32:43.961Z
Request finished GET https:///warmup - 200 - text/plain;+charset=utf-8 476.4169ms
2026-02-01T20:32:43.962Z
warn: Amazon.Lambda.AspNetCoreServer.AbstractAspNetCoreFunction[0]
2026-02-01T20:32:43.962Z
Request does not contain domain name information but is derived from APIGatewayProxyFunction.
2026-02-01T20:32:43.962Z
info: Microsoft.AspNetCore.Hosting.Diagnostics[1]
2026-02-01T20:32:43.962Z
Request starting GET https:///warmup - - 0
2026-02-01T20:32:43.962Z
info: Microsoft.AspNetCore.Routing.EndpointMiddleware[0]
2026-02-01T20:32:43.962Z
Executing endpoint 'HTTP: GET /warmup'
2026-02-01T20:32:43.963Z
info: Microsoft.AspNetCore.Routing.EndpointMiddleware[1]
2026-02-01T20:32:43.963Z
Executed endpoint 'HTTP: GET /warmup'
2026-02-01T20:32:43.963Z
info: Microsoft.AspNetCore.Hosting.Diagnostics[2]
2026-02-01T20:32:43.963Z
Request finished GET https:///warmup - 200 - text/plain;+charset=utf-8 0.3481ms
2026-02-01T20:32:43.963Z
warn: Amazon.Lambda.AspNetCoreServer.AbstractAspNetCoreFunction[0]
2026-02-01T20:32:43.963Z
Request does not contain domain name information but is derived from APIGatewayProxyFunction.
2026-02-01T20:32:43.963Z
info: Microsoft.AspNetCore.Hosting.Diagnostics[1]
2026-02-01T20:32:43.963Z
Request starting GET https:///warmup - - 0
2026-02-01T20:32:43.963Z
info: Microsoft.AspNetCore.Routing.EndpointMiddleware[0]
2026-02-01T20:32:43.963Z
Executing endpoint 'HTTP: GET /warmup'
2026-02-01T20:32:43.963Z
info: Microsoft.AspNetCore.Routing.EndpointMiddleware[1]
2026-02-01T20:32:43.963Z
Executed endpoint 'HTTP: GET /warmup'
2026-02-01T20:32:43.963Z
info: Microsoft.AspNetCore.Hosting.Diagnostics[2]
2026-02-01T20:32:43.963Z
Request finished GET https:///warmup - 200 - text/plain;+charset=utf-8 0.0992ms
2026-02-01T20:32:43.963Z
warn: Amazon.Lambda.AspNetCoreServer.AbstractAspNetCoreFunction[0]
2026-02-01T20:32:43.963Z
Request does not contain domain name information but is derived from APIGatewayProxyFunction.
2026-02-01T20:32:43.963Z
info: Microsoft.AspNetCore.Hosting.Diagnostics[1]
2026-02-01T20:32:43.963Z
Request starting GET https:///warmup - - 0
2026-02-01T20:32:43.963Z
info: Microsoft.AspNetCore.Routing.EndpointMiddleware[0]
2026-02-01T20:32:43.963Z
Executing endpoint 'HTTP: GET /warmup'
2026-02-01T20:32:43.963Z
info: Microsoft.AspNetCore.Routing.EndpointMiddleware[1]
2026-02-01T20:32:43.963Z
Executed endpoint 'HTTP: GET /warmup'
2026-02-01T20:32:43.963Z
info: Microsoft.AspNetCore.Hosting.Diagnostics[2]
2026-02-01T20:32:43.963Z
Request finished GET https:///warmup - 200 - text/plain;+charset=utf-8 0.0664ms
2026-02-01T20:32:43.963Z
warn: Amazon.Lambda.AspNetCoreServer.AbstractAspNetCoreFunction[0]
2026-02-01T20:32:43.963Z
Request does not contain domain name information but is derived from APIGatewayProxyFunction.
2026-02-01T20:32:43.963Z
info: Microsoft.AspNetCore.Hosting.Diagnostics[1]
2026-02-01T20:32:43.963Z
Request starting GET https:///warmup - - 0
2026-02-01T20:32:43.963Z
info: Microsoft.AspNetCore.Routing.EndpointMiddleware[0]
2026-02-01T20:32:43.963Z
Executing endpoint 'HTTP: GET /warmup'
2026-02-01T20:32:43.963Z
info: Microsoft.AspNetCore.Routing.EndpointMiddleware[1]
2026-02-01T20:32:43.963Z
Executed endpoint 'HTTP: GET /warmup'
2026-02-01T20:32:43.963Z
info: Microsoft.AspNetCore.Hosting.Diagnostics[2]
2026-02-01T20:32:43.963Z
Request finished GET https:///warmup - 200 - text/plain;+charset=utf-8 0.0804ms
2026-02-01T20:32:44.144Z
INIT_REPORT Init Duration: 1970.07 ms
2026-02-01T20:32:44.181Z
INIT_REPORT Init Duration: 1975.76 ms

Cold Start after 10 minutes of no requests:

2026-02-01T20:43:52.318Z
INIT_START Runtime Version: dotnet:10.v20 Runtime Version ARN: arn:aws:lambda:us-east-1::runtime:1b485095a08c766eafbff6b853f6e32d7a9fd64469bb1d0b1312a9e324113ea8
2026-02-01T20:43:52.844Z
START RequestId: 1a38fbf8-46ee-49aa-ae5c-1188f2c10afb Version: $LATEST
2026-02-01T20:43:53.097Z
info: Microsoft.AspNetCore.Hosting.Diagnostics[1]
2026-02-01T20:43:53.097Z
Request starting GET https://xyz.lambda-url.us-east-1.on.aws/v1.0/Utilities/GetStatusMessageToUser - - 0
2026-02-01T20:43:53.709Z
info: Microsoft.AspNetCore.Routing.EndpointMiddleware[0]
2026-02-01T20:43:53.709Z
Executing endpoint 'HTTP: GET v{version:apiVersion}/Utilities/GetStatusMessageToUser => GetStatusMessageToUser'
2026-02-01T20:43:57.837Z
info: Microsoft.EntityFrameworkCore.Database.Command[20101]
2026-02-01T20:43:57.837Z
Executed DbCommand (76ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
2026-02-01T20:43:57.837Z
SELECT `s`.`MessageId`, `s`.`Adddate`, `s`.`Message`, `s`.`MessageEnabled`
2026-02-01T20:43:57.837Z
FROM `StatusMessageToUser` AS `s`
2026-02-01T20:43:57.837Z
WHERE `s`.`MessageEnabled`
2026-02-01T20:43:57.837Z
LIMIT 1
2026-02-01T20:43:57.973Z
info: Microsoft.AspNetCore.Http.Result.OkObjectResult[1]
2026-02-01T20:43:57.973Z
Setting HTTP status code 200.
2026-02-01T20:43:57.977Z
info: Microsoft.AspNetCore.Http.Result.OkObjectResult[3]
2026-02-01T20:43:57.977Z
Writing value of type 'StatusMessageToUserDto' as Json.
2026-02-01T20:43:58.013Z
info: Microsoft.AspNetCore.Routing.EndpointMiddleware[1]
2026-02-01T20:43:58.013Z
Executed endpoint 'HTTP: GET v{version:apiVersion}/Utilities/GetStatusMessageToUser => GetStatusMessageToUser'
2026-02-01T20:43:58.057Z
info: Microsoft.AspNetCore.Hosting.Diagnostics[2]
2026-02-01T20:43:58.057Z
Request finished GET https://xyz.lambda-url.us-east-1.on.aws/v1.0/Utilities/GetStatusMessageToUser - 200 - application/json;+charset=utf-8 4958.2651ms
2026-02-01T20:43:58.169Z
END RequestId: 1a38fbf8-46ee-49aa-ae5c-1188f2c10afb
2026-02-01T20:43:58.169Z
REPORT RequestId: 1a38fbf8-46ee-49aa-ae5c-1188f2c10afb Duration: 5310.57 ms Billed Duration: 5834 ms Memory Size: 512 MB Max Memory Used: 154 MB Init Duration: 522.85 ms

AWS .NET SDK and/or Package version used

Amazon.Lambda.AspNetCoreServer.Hosting: 1.9.1

Targeted .NET Platform

.NET 10 (Minimal API)

Operating System and version

OSX

[mikemike396]

One update:

So adding a function URL to the alias seems to be triggering RESTORE_START.

We're still seeing slower than expected time compared to when back to back requests are made to the Lambda function. Is this something untreated to SnapStart at this point? The gap seems to be between Request Starting and the DB Command.

2026-02-01T21:08:37.050Z
RESTORE_START Runtime Version: dotnet:10.v20 Runtime Version ARN: arn:aws:lambda:us-east-1::runtime:1b485095a08c766eafbff6b853f6e32d7a9fd64469bb1d0b1312a9e324113ea8
2026-02-01T21:08:38.409Z
RESTORE_REPORT Restore Duration: 1384.30 ms
2026-02-01T21:08:38.423Z
START RequestId: 1b423507-5e88-4b52-a65a-a9760065d3f3 Version: 11
2026-02-01T21:08:38.644Z
info: Microsoft.AspNetCore.Hosting.Diagnostics[1]
2026-02-01T21:08:38.644Z
Request starting GET https://xyz-url.us-east-1.on.aws/v1.0/Utilities/GetStatusMessageToUser - - 0
2026-02-01T21:08:38.760Z
info: Microsoft.AspNetCore.Routing.EndpointMiddleware[0]
2026-02-01T21:08:38.760Z
Executing endpoint 'HTTP: GET v{version:apiVersion}/Utilities/GetStatusMessageToUser => GetStatusMessageToUser'
2026-02-01T21:08:44.306Z
info: Microsoft.EntityFrameworkCore.Database.Command[20101]
2026-02-01T21:08:44.306Z
Executed DbCommand (60ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
2026-02-01T21:08:44.306Z
SELECT `s`.`MessageId`, `s`.`Adddate`, `s`.`Message`, `s`.`MessageEnabled`
2026-02-01T21:08:44.306Z
FROM `StatusMessageToUser` AS `s`
2026-02-01T21:08:44.306Z
WHERE `s`.`MessageEnabled`
2026-02-01T21:08:44.306Z
LIMIT 1
2026-02-01T21:08:44.445Z
info: Microsoft.AspNetCore.Http.Result.OkObjectResult[1]
2026-02-01T21:08:44.445Z
Setting HTTP status code 200.
2026-02-01T21:08:44.460Z
info: Microsoft.AspNetCore.Http.Result.OkObjectResult[3]
2026-02-01T21:08:44.460Z
Writing value of type 'StatusMessageToUserDto' as Json.
2026-02-01T21:08:44.465Z
info: Microsoft.AspNetCore.Routing.EndpointMiddleware[1]
2026-02-01T21:08:44.465Z
Executed endpoint 'HTTP: GET v{version:apiVersion}/Utilities/GetStatusMessageToUser => GetStatusMessageToUser'
2026-02-01T21:08:44.503Z
info: Microsoft.AspNetCore.Hosting.Diagnostics[2]
2026-02-01T21:08:44.503Z
Request finished GET https://xyz-url.us-east-1.on.aws/v1.0/Utilities/GetStatusMessageToUser - 200 - application/json;+charset=utf-8 5858.6734ms
2026-02-01T21:08:44.620Z
END RequestId: 1b423507-5e88-4b52-a65a-a9760065d3f3
2026-02-01T21:08:44.621Z
REPORT RequestId: 1b423507-5e88-4b52-a65a-a9760065d3f3 Duration: 6197.74 ms Billed Duration: 6519 ms Memory Size: 512 MB Max Memory Use

[mikemike396]

Closing this out as it seems like a MySql / DB connection issue, we ended up moving to Elastic Beanstalk running our container on EC2. Thank you!

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