Docker auto-scale and asleep motd status by Lenart12 · Pull Request #488 · itzg/mc-router

Lenart12 · 2025-12-09T05:19:06Z

No description provided.

…vers

Copilot

Pull request overview

This PR adds Docker auto-scale functionality to enable scale-to-zero behavior for Docker containers, similar to the existing Kubernetes auto-scale feature. The implementation allows mc-router to automatically start/unpause stopped containers when clients connect and gracefully stop containers after a configurable idle period.

Key changes:

Refactored ScalerFunc into WakerFunc (returns endpoint string) and SleeperFunc to support dynamic endpoint resolution after container startup
Implemented Docker container start/stop/unpause operations with health check waiting
Added per-container auto-scale label overrides (mc-router.auto-scale-up and mc-router.auto-scale-down)

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
server/routes.go	Refactored type signatures from `ScalerFunc` to `WakerFunc`/`SleeperFunc`; added guard to prevent downscaler activation on empty backends
server/k8s.go	Updated K8s integration to wrap scale-up function and return endpoint; updated type signatures
server/docker_swarm.go	Updated Docker Swarm signatures to match new types (auto-scale not yet implemented for Swarm)
server/docker.go	Implemented full Docker auto-scale with container start/stop/unpause, health checking, and route updates; added global state for container tracking
server/connector.go	Updated waker invocation to handle returned endpoint and improved error handling/logging
server/server.go	Extended downscaler enablement check to include Docker environments
server/api_server.go	Updated API route creation to use new empty function names
README.md	Added comprehensive documentation for Docker auto-scale feature with examples

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server/docker.go

server/k8s.go

server/docker.go

…multiple hosts

Copilot

Pull request overview

Copilot reviewed 12 out of 12 changed files in this pull request and generated 9 comments.

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server/docker.go

server/routes.go

server/docker.go

server/down_scaler.go

server/docker.go

server/down_scaler.go

server/docker.go

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Pull request overview

Copilot reviewed 12 out of 12 changed files in this pull request and generated 4 comments.

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server/docker.go

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Copilot reviewed 16 out of 16 changed files in this pull request and generated 3 comments.

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server/k8s_test.go

server/connector.go

server/configs.go

Lenart12 · 2025-12-09T14:16:56Z

This is ready for review. I didn't notice #406 is trying to merge about the same functionality.

itzg · 2025-12-09T18:00:41Z

Thanks. I was about to ask if you were finished addressing the copilot feedback.

Don't worry about overlap with the other PR. Yours has a more focused scope that addresses a common and immediate need. The other PR grew a bit broad, which is partly why it is parked there (and because I keep forgetting about it).

Lenart12 · 2025-12-10T20:52:21Z

Added a fix that showed default asleep motd on nonexistent routes.

itzg · 2025-12-14T15:44:40Z

Sorry for the delay with me reviewing this. I've set a goal for myself to look over it today. When I skimmed the changes they looked good, but wanted to take a better look while looking on a computer monitor.

itzg

Great contribution. Just some nitpicky things.

itzg · 2025-12-14T16:12:58Z

mcproto/types.go

 	PacketIdLogin                = 0x00 // during StateLogin
 	PacketIdLegacyServerListPing = 0xFE
+	PacketIdStatusRequest        = 0x00
+	PacketIdStatusPing           = 0x01


Please call this PacketIdPingRequest to match the docs naming convention:

https://minecraft.wiki/w/Java_Edition_protocol/Packets#Ping_Request_(status)

I wasn't able to find a "status ping" when searching the page as is.

itzg · 2025-12-14T16:13:50Z

mcproto/types.go


+// PingPayload represents the status ping payload (packet 0x01)
+type PingPayload struct {
+	Value int64


This field name should be Timestamp, right? According to

https://minecraft.wiki/w/Java_Edition_protocol/Packets#Ping_Request_(status)

itzg · 2025-12-14T16:19:02Z

mcproto/read.go

+		case PacketIdStatusPing:
+			// read 8-byte long from remainder
+			if remainder.Len() >= 8 {
+				val := int64(binary.BigEndian.Uint64(remainder.Next(8)))


Use the existing ReadLong function in this package

itzg · 2025-12-14T16:20:34Z

mcproto/write.go

+// StatusResponse is a minimal structure for the status JSON
+type StatusResponse struct {
+	Version struct {
+		Name     string `json:"name"`
+		Protocol int    `json:"protocol"`
+	} `json:"version"`
+	Players struct {
+		Max    int `json:"max"`
+		Online int `json:"online"`
+		Sample []struct {
+			Name string `json:"name"`
+			ID   string `json:"id"`
+		} `json:"sample,omitempty"`
+	} `json:"players"`
+	Description        map[string]interface{} `json:"description"`
+	Favicon            string                 `json:"favicon,omitempty"`
+	EnforcesSecureChat *bool                  `json:"enforcesSecureChat,omitempty"`
+}


Move to types.go

itzg · 2025-12-14T16:21:06Z

mcproto/write.go

+	if err := WriteString(&payload, jsonString); err != nil {
+		return err
+	}
+	pkt := buildPacket(0x00, payload.Bytes())


Declare const for the packet ID 0x00 here

itzg · 2025-12-14T16:21:28Z

mcproto/write.go

+	var buf [8]byte
+	binary.BigEndian.PutUint64(buf[:], uint64(payload))
+	pl.Write(buf[:])
+	pkt := buildPacket(0x01, pl.Bytes())


Declare packet ID const

itzg · 2025-12-14T16:51:38Z

server/connector.go

+		logrus.WithFields(logrus.Fields{
+			"client": frontendConn.RemoteAddr(),
+			"error":  err,
+		}).Debug("Predefined status: error reading initial status packet")


Perhaps should be Warn level

itzg · 2025-12-14T17:07:55Z

server/docker.go

-	client *client.Client
+	config           dockerWatcherConfig
+	client           *client.Client
+	dockerRoutesLock sync.RWMutex


I'm wondering why the extra mutex? It looks like the mutex field on L64 isn't even used, so perhaps removing that is the cleaner solution.

Leftover from initial development... whoops

server/docker.go

itzg · 2025-12-14T17:35:16Z

server/docker.go

 		}
+		if key == DockerRouterLabelAutoScaleUp {
+			lowerValue := strings.TrimSpace(strings.ToLower(value))
+			data.autoScaleUp = lowerValue != "" && lowerValue != "0" && lowerValue != "false" && lowerValue != "no"


It would be great to create a helper function for this and then use the same at

mc-router/server/k8s.go

Lines 287 to 291 in 22ec39b

enabled, exists := service.Annotations[AnnotationAutoScaleUp]

if exists {

if enabled == "false" {

return nil

}

and below at L385

Used strconv.ParseBool instead of a new helper function.

itzg · 2025-12-20T14:25:22Z

While doing some sanity testing, using examples/docker-discovery/compose.yml, I thought I'd change the mc-router.host to a usable hostname and did a docker compose up. That recreated/started both servers there. It seems like after that it detects the new container instance but isn't able to verify connectivity after "waking it up"

time="2025-12-20T08:18:55-06:00" level=debug msg="Got connection" client="127.0.0.1:57509"
time="2025-12-20T08:18:55-06:00" level=debug msg="Read frame length" client="127.0.0.1:57509" length=24
time="2025-12-20T08:18:55-06:00" level=debug msg="Reading frame content" client="127.0.0.1:57509" length=24 total=24
time="2025-12-20T08:18:55-06:00" level=debug msg="Read frame" client="127.0.0.1:57509" frame="Frame:[len=24, payload=0X008606116C6F63616C686F73742E69747A672E6D6563DD02]"
time="2025-12-20T08:18:55-06:00" level=debug msg="Read packet" client="127.0.0.1:57509" packet="Frame:[len=25, packetId=0, data=0X8606116C6F63616C686F73742E69747A672E6D6563DD02]"
time="2025-12-20T08:18:55-06:00" level=debug msg="Got packet" client="127.0.0.1:57509" length=25 packetID=0
time="2025-12-20T08:18:55-06:00" level=debug msg="Got handshake" client="127.0.0.1:57509" handshake="&{774 localhost.itzg.me 25565 2}"
time="2025-12-20T08:18:55-06:00" level=debug msg="Read frame length" client="127.0.0.1:57509" length=22
time="2025-12-20T08:18:55-06:00" level=debug msg="Reading frame content" client="127.0.0.1:57509" length=22 total=22
time="2025-12-20T08:18:55-06:00" level=debug msg="Read frame" client="127.0.0.1:57509" frame="Frame:[len=22, payload=0X000469747A675CDDFD26FC864981B52EC42BB10BFDEF]"
time="2025-12-20T08:18:55-06:00" level=debug msg="Read packet" client="127.0.0.1:57509" packet="Frame:[len=23, packetId=0, data=0X0469747A675CDDFD26FC864981B52EC42BB10BFDEF]"
time="2025-12-20T08:18:55-06:00" level=debug msg="Got user info" client="127.0.0.1:57509" player=itzg/5cddfd26-fc86-4981-b52e-c42bb10bfdef
time="2025-12-20T08:18:55-06:00" level=debug msg="Finding backend for server address" serverAddress=localhost.itzg.me
time="2025-12-20T08:18:55-06:00" level=debug msg="checked if player is allowed to wake up the server" client="127.0.0.1:57509" player=itzg/5cddfd26-fc86-4981-b52e-c42bb10bfdef server=localhost.itzg.me serverAllowsPlayer=true
time="2025-12-20T08:18:55-06:00" level=info msg="Waking up backend server" serverAddress=localhost.itzg.me
time="2025-12-20T08:19:17-06:00" level=error msg="failed to wake up backend" error="timeout waiting for container to become reachable at 172.18.0.2:25565" serverAddress=localhost.itzg.me
time="2025-12-20T08:19:17-06:00" level=info msg="Closed connection to backend" backendHostPort="172.18.0.2:25565" client="127.0.0.1:57475" connectionCount=0
time="2025-12-20T08:19:17-06:00" level=debug msg="Beginning scale down" backendEndpoint="172.18.0.2:25565"
time="2025-12-20T08:19:17-06:00" level=debug msg="Closing frontend connection" client="127.0.0.1:57475"
time="2025-12-20T08:19:56-06:00" level=error msg="failed to wake up backend" error="timeout waiting for container to become reachable at 172.18.0.2:25565" serverAddress=localhost.itzg.me
time="2025-12-20T08:19:56-06:00" level=info msg="Closed connection to backend" backendHostPort="172.18.0.2:25565" client="127.0.0.1:57509" connectionCount=0
time="2025-12-20T08:19:56-06:00" level=debug msg="Beginning scale down" backendEndpoint="172.18.0.2:25565"
time="2025-12-20T08:19:56-06:00" level=debug msg="Closing frontend connection" client="127.0.0.1:57509"

itzg · 2025-12-20T14:30:30Z

Disregard that comment. My testing scenario was flawed since I'm running mc-router outside of docker.

itzg

Excellent! Thanks.

itzg · 2025-12-20T15:35:10Z

Can you take a look at the unit test failure:

https://github.com/itzg/mc-router/actions/runs/20274437941/job/58612175899?pr=488

…ress

Lenart12 · 2025-12-20T16:19:46Z

Tests were failing because some method signatures changed and were used for running k8s tests. I checked all tests now pass and I have also added some Docker compose examples.

itzg · 2025-12-20T19:55:07Z

Released in https://github.com/itzg/mc-router/releases/tag/v1.38.0

Lenart12 added 3 commits December 9, 2025 06:07

Split ScalerFunc to Waker and Sleeper

f7a00ac

Implement docker scale to zero

f4c47c4

Update readme to include Docker auto-scaling features for backend ser…

7314b88

…vers

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Lenart12 added 3 commits December 9, 2025 10:55

Implement Copilot suggestions

e2048a4

Add waker and sleeper for default routes

6228492

Down scale based on backend endpoint to prevent scaling servers with …

93f880f

…multiple hosts

Lenart12 requested a review from Copilot December 9, 2025 11:18

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Lenart12 added 4 commits December 9, 2025 13:08

Check all fields for change in Docker monitoring

ad1f858

Show server asleep status when backend offline

113be4e

Allow setting asleep motd from docker label

f7afe89

Update readme to show asleep motd configuration

0bce91b

Lenart12 requested a review from Copilot December 9, 2025 14:04

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Lenart12 changed the title ~~Docker auto-scale~~ Docker auto-scale and asleep motd status Dec 9, 2025

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Minor fixes

710a1df

fix: Only show asleep status on servers with a route

1c846a5

itzg reviewed Dec 14, 2025

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Lenart12 added 3 commits December 16, 2025 17:02

style: Rename and move some variables to be more consistent with mcproto

aa4363a

chore: Remove unused mutex

b1843f6

fix: Use consistent bool parsing for service/container labels

ee67c5c

Lenart12 requested a review from itzg December 16, 2025 16:05

itzg previously approved these changes Dec 20, 2025

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Lenart12 added 3 commits December 20, 2025 16:50

fix: Update mocked methods in K8s tests to match new signatures

eeb377d

fix: Fix nil pointer crash in Test_routesImpl_FindBackendForServerAdd…

41c4ae2

…ress

feat: Add docker compose examples for Docker auto-scale

045f353

Lenart12 dismissed itzg’s stale review via 045f353 December 20, 2025 16:17

Lenart12 requested a review from itzg December 20, 2025 16:19

itzg merged commit 4dff00d into itzg:main Dec 20, 2025
4 checks passed

This was referenced Dec 21, 2025

With k8s correctly handle disabled auto-scale up case #495

Merged

Update devcontainer to support docker auto-discovery #501

Merged

	enabled, exists := service.Annotations[AnnotationAutoScaleUp]
	if exists {
	if enabled == "false" {
	return nil
	}

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Lenart12 commented Dec 9, 2025

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itzg commented Dec 9, 2025

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itzg commented Dec 14, 2025

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