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Copyright (c) 2026, Pim van Pelt <pim@ipng.ch>
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
1. Redistributions of source code must retain the above copyright notice, this
list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright notice,
this list of conditions and the following disclaimer in the documentation
and/or other materials provided with the distribution.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

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# maglevd
Health checker and gRPC control plane for VPP Maglev load balancing.
## Build
```sh
make # builds bin/maglevd
make test # runs all tests
make proto # regenerates gRPC stubs from proto/maglev.proto
```
Requires Go 1.25+ and (for `make proto`) `protoc` with `protoc-gen-go` and `protoc-gen-go-grpc`.
## Run
```sh
maglevd --config /etc/maglev/maglev.yaml --grpc-addr :9090
```
| Flag | Env | Default |
|---|---|---|
| `--config` | `MAGLEV_CONFIG` | `/etc/maglev/frontend.yaml` |
| `--grpc-addr` | `MAGLEV_GRPC_ADDR` | `:9090` |
| `--log-level` | `MAGLEV_LOG_LEVEL` | `info` |
Send `SIGHUP` to reload the config without restarting. Backends whose health-check config is
unchanged continue probing uninterrupted.
`maglevd` requires `CAP_NET_RAW` to open raw ICMP sockets.
## Minimal config
```yaml
maglev:
healthchecks:
http:
type: http
port: 80
params:
path: /healthz
interval: 2s
timeout: 3s
backends:
web0: {address: 192.0.2.10, healthcheck: http}
web1: {address: 192.0.2.11, healthcheck: http}
frontends:
web:
address: 192.0.2.1
protocol: tcp
port: 80
backends: [web0, web1]
```
See [docs/config-guide.md](docs/config-guide.md) for the full configuration reference.
## Docker
```sh
docker build -t maglevd .
docker run --cap-add NET_RAW -v /etc/maglev:/etc/maglev maglevd
```

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// Copyright (c) 2026, Pim van Pelt <pim@ipng.ch>
package main package main
import ( import (

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# maglevd Configuration Guide
## Overview
`maglevd` consumes a YAML configuration file of a specific format. Validation is performed
in two stages:
1. **Structural parsing**: the YAML is unmarshalled into typed Go structs. Unknown fields and
type mismatches are rejected immediately.
1. **Semantic validation**: cross-field and cross-object rules are enforced, for example
ensuring that every backend referenced by a frontend exists, that address families are
consistent within a frontend, and that IP source addresses are the correct family.
If you want to get started quickly, take a look at the [example config](#example).
## Basic structure
The YAML configuration file has the following top-level structure:
```yaml
maglev:
healthchecker:
[ Global health checker settings ]
healthchecks:
my-check:
[ Health check definition ]
backends:
my-backend:
[ Backend definition ]
frontends:
my-frontend:
[ Frontend (VIP) definition ]
```
All four sections live under the top-level `maglev:` key. The `healthchecks`, `backends`,
and `frontends` sections are maps keyed by an arbitrary name of your choosing. Names must be
unique within their section and are case-sensitive.
---
## healthchecker
Global settings for the health checker engine.
* ***transition-history***: An integer >= 1 that controls how many state transitions are
retained per backend for display via the gRPC API. Defaults to `5`.
* ***netns***: The name of a Linux network namespace in which probes are executed. When
empty or omitted, probes run in the current (default) network namespace. Useful when
backends are reachable only through a dedicated dataplane namespace.
Example:
```yaml
maglev:
healthchecker:
transition-history: 10
netns: dataplane
```
---
## healthchecks
A named map of health check definitions. Each health check describes *how* to probe a backend.
Backends reference health checks by name. The same health check can be reused across any number
of backends; each backend is probed exactly once regardless of how many frontends reference it.
Common fields (all types):
* ***type***: Required. One of `icmp`, `tcp`, `http`, or `https`.
* ***port***: The destination port to probe. Required for `tcp`, `http`, and `https`.
Must be omitted for `icmp`.
* ***probe-ipv4-src***: An optional IPv4 source address used when probing IPv4 backends.
Must be an IPv4 address. When omitted, the OS chooses the source address.
* ***probe-ipv6-src***: An optional IPv6 source address used when probing IPv6 backends.
Must be an IPv6 address. When omitted, the OS chooses the source address.
* ***interval***: Required. A positive Go duration string (e.g. `2s`, `500ms`) controlling
how often a probe is sent when the backend is fully healthy or in the initial unknown state.
* ***fast-interval***: Optional. A positive duration used instead of `interval` while the
backend's health counter is degraded (between down and up). When omitted, `interval` is used.
* ***down-interval***: Optional. A positive duration used instead of `interval` while the
backend is fully down. When omitted, `interval` is used. Setting this to a longer value
reduces probe traffic to backends that are known to be offline.
* ***timeout***: Required. A positive duration after which an in-flight probe is abandoned
and counted as a failure.
* ***rise***: The number of consecutive successes required to transition from down to up.
Defaults to `2`. Must be >= 1.
* ***fall***: The number of consecutive failures required to transition from up to down.
Defaults to `3`. Must be >= 1.
### type: icmp
Sends an ICMP echo request (ping) to the backend address. Requires `CAP_NET_RAW`. No `port`
may be specified. No `params` block is used.
```yaml
healthchecks:
ping:
type: icmp
probe-ipv4-src: 10.0.0.1
probe-ipv6-src: 2001:db8::1
interval: 2s
timeout: 1s
rise: 2
fall: 3
```
### type: tcp
Opens a TCP connection to the backend and immediately closes it upon success. Use `params` to
optionally wrap the connection in TLS.
* ***params.ssl***: A boolean. When `true`, a TLS handshake is performed after the TCP
connection is established. Defaults to `false`.
* ***params.server-name***: The TLS SNI hostname sent during the handshake. When omitted,
the backend IP address is used.
* ***params.insecure-skip-verify***: A boolean. When `true`, the TLS certificate presented
by the server is not verified. Defaults to `false`.
```yaml
healthchecks:
imaps-check:
type: tcp
port: 993
params:
ssl: true
server-name: imaps.example.com
interval: 5s
timeout: 3s
rise: 2
fall: 3
```
### type: http / https
Opens a TCP (or TLS for `https`) connection, sends an HTTP request, and evaluates the response
code. An optional regexp can additionally match against the response body.
* ***params.path***: Required. The HTTP request path, e.g. `/healthz`.
* ***params.host***: The `Host` header value sent in the request. When omitted, the backend
IP address is used.
* ***params.response-code***: The expected HTTP response code. Can be a single value (`"200"`)
or an inclusive range (`"200-299"`). Defaults to `"200"`.
* ***params.response-regexp***: An optional Go regular expression matched against the response
body. If specified, the body must match for the probe to succeed.
* ***params.server-name***: The TLS SNI hostname (`https` only). Defaults to the value of
`params.host` if not set.
* ***params.insecure-skip-verify***: A boolean. Skip TLS certificate verification (`https`
only). Defaults to `false`.
```yaml
healthchecks:
nginx-http:
type: http
port: 80
params:
path: /healthz
host: nginx.example.com
response-code: "200-204"
interval: 2s
fast-interval: 500ms
down-interval: 30s
timeout: 3s
rise: 2
fall: 3
nginx-https:
type: https
port: 443
params:
path: /healthz
host: nginx.example.com
server-name: nginx.example.com
insecure-skip-verify: false
interval: 5s
timeout: 3s
```
---
## backends
A named map of individual backend servers. Each backend has a single IP address and optionally
references a health check by name. Backends are probed exactly once, even if they appear in
multiple frontends.
* ***address***: Required. The IPv4 or IPv6 address of this backend server.
* ***healthcheck***: The name of a health check defined in the `healthchecks` section.
When empty or omitted, no probing is performed and the backend is assumed permanently
healthy. This is useful for backends that are always available or managed by other means.
* ***enabled***: A boolean controlling whether this backend participates in any frontend.
When `false`, the backend is excluded entirely and no probe goroutine is started.
Defaults to `true`.
* ***weight***: An integer between 0 and 100 (inclusive) expressing the relative weight of
this backend in a frontend's pool. `0` keeps the backend in the pool but assigns it no
traffic. Defaults to `100`.
Examples:
```yaml
backends:
nginx0-ams:
address: 198.51.100.10
healthcheck: nginx-http
nginx0-lon:
address: 198.51.100.11
healthcheck: nginx-http
weight: 50
nginx0-draining:
address: 198.51.100.12
healthcheck: nginx-http
enabled: false
static-backend:
address: 198.51.100.20
# no healthcheck: assumed always healthy
```
---
## frontends
A named map of virtual IPs (VIPs). Each frontend ties together a listener address with a set
of backends. The gRPC API exposes frontends by name.
* ***description***: An optional free-text string for documentation purposes.
* ***address***: Required. The IPv4 or IPv6 address of the VIP.
* ***protocol***: The IP protocol, either `tcp` or `udp`. When omitted, the frontend matches
all traffic to the VIP address regardless of protocol. If `port` is specified, `protocol`
must also be set.
* ***port***: The destination port of the VIP, an integer between 1 and 65535. Requires
`protocol` to be set. When omitted, the frontend matches all ports. Note that the
frontend port is independent of the healthcheck port: a frontend on port 443 may use
a healthcheck that probes port 80.
* ***backends***: Required. A non-empty list of backend names. All backends in a frontend
must have addresses of the same address family (all IPv4 or all IPv6). Every name must
refer to an existing entry in the `backends` section.
Examples:
```yaml
frontends:
nginx-v4-http:
description: "IPv4 HTTP VIP"
address: 198.51.100.1
protocol: tcp
port: 80
backends: [nginx0-ams, nginx0-lon]
nginx-v4-https:
description: "IPv4 HTTPS VIP — reuses the same backends as HTTP"
address: 198.51.100.1
protocol: tcp
port: 443
backends: [nginx0-ams, nginx0-lon]
maildrop-imaps:
description: "IMAPS VIP"
address: 2001:db8::1
protocol: tcp
port: 993
backends: [maildrop0-ams, maildrop0-lon]
catchall:
description: "Match all traffic to this VIP regardless of protocol or port"
address: 198.51.100.2
backends: [static-backend]
```
---
## Example
A complete configuration tying all sections together:
```yaml
maglev:
healthchecker:
transition-history: 5
netns: dataplane
healthchecks:
nginx:
type: http
port: 80
params:
path: /healthz
host: nginx.example.com
response-code: "200"
interval: 2s
fast-interval: 500ms
down-interval: 30s
timeout: 3s
rise: 2
fall: 3
dovecot:
type: tcp
port: 993
params:
ssl: true
server-name: imaps.example.com
interval: 5s
fast-interval: 1s
down-interval: 30s
timeout: 3s
rise: 2
fall: 3
ping6:
type: icmp
probe-ipv6-src: 2001:db8:probe::1
interval: 2s
timeout: 1s
backends:
nginx0-ams:
address: 198.51.100.10
healthcheck: nginx
nginx0-lon:
address: 198.51.100.11
healthcheck: nginx
nginx0-fra:
address: 198.51.100.12
healthcheck: nginx
weight: 50
maildrop0-ams:
address: 2001:db8:1::10
healthcheck: dovecot
maildrop0-lon:
address: 2001:db8:1::11
healthcheck: dovecot
frontends:
nginx-http:
description: "HTTP VIP"
address: 198.51.100.1
protocol: tcp
port: 80
backends: [nginx0-ams, nginx0-lon, nginx0-fra]
nginx-https:
description: "HTTPS VIP — same backends, different port"
address: 198.51.100.1
protocol: tcp
port: 443
backends: [nginx0-ams, nginx0-lon, nginx0-fra]
maildrop-imaps:
description: "IMAPS VIP"
address: 2001:db8::1
protocol: tcp
port: 993
backends: [maildrop0-ams, maildrop0-lon]
```

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// Copyright (c) 2026, Pim van Pelt <pim@ipng.ch>
package checker package checker
import ( import (

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// Copyright (c) 2026, Pim van Pelt <pim@ipng.ch>
package checker package checker
import ( import (

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// Copyright (c) 2026, Pim van Pelt <pim@ipng.ch>
package config package config
import ( import (

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// Copyright (c) 2026, Pim van Pelt <pim@ipng.ch>
package config package config
import ( import (

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// Copyright (c) 2026, Pim van Pelt <pim@ipng.ch>
package grpcapi package grpcapi
import ( import (

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// Copyright (c) 2026, Pim van Pelt <pim@ipng.ch>
package grpcapi package grpcapi
import ( import (

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// Copyright (c) 2026, Pim van Pelt <pim@ipng.ch>
package health package health
import ( import (

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// Copyright (c) 2026, Pim van Pelt <pim@ipng.ch>
package health package health
import ( import (

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// Copyright (c) 2026, Pim van Pelt <pim@ipng.ch>
package prober package prober
import ( import (

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// Copyright (c) 2026, Pim van Pelt <pim@ipng.ch>
package prober package prober
import ( import (

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// Copyright (c) 2026, Pim van Pelt <pim@ipng.ch>
package prober package prober
import ( import (

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// Copyright (c) 2026, Pim van Pelt <pim@ipng.ch>
package prober package prober
import ( import (

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// Copyright (c) 2026, Pim van Pelt <pim@ipng.ch>
package prober package prober
import ( import (

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// Copyright (c) 2026, Pim van Pelt <pim@ipng.ch>
package prober package prober
import ( import (

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// Copyright (c) 2026, Pim van Pelt <pim@ipng.ch>
package prober package prober
import ( import (