vpp-maglev/docs/user-guide.md

User Guide

maglevd

maglevd is the health-checker daemon. It probes backends according to the configuration file, maintains their health state, and exposes a gRPC API for inspection and control.

Flags

Flag	Environment variable	Default	Description
--config	MAGLEV_CONFIG	/etc/vpp-maglev/maglev.yaml	Path to the YAML configuration file.
--grpc-addr	MAGLEV_GRPC_ADDR	:9090	TCP address on which the gRPC server listens.
--log-level	MAGLEV_LOG_LEVEL	info	Log verbosity: debug, info, warn, or error.
--check	—	—	Read and validate the config file, then exit. Exits 0 if the config is valid, 1 on YAML parse error, 2 on semantic error.
--reflection	—	true	Enable gRPC server reflection. Allows grpcurl to introspect the API without the .proto file. Set to false to disable.
--version	—	—	Print version, commit hash, and build date, then exit.

Flags take precedence over environment variables. Both are optional; defaults are used for anything not set.

Signals

Signal	Effect
SIGHUP	Reload the configuration file. The file is checked before applying; if there is a parse or semantic error the reload is aborted and the error is logged (the daemon continues running with its current config). New backends are started, removed backends are stopped, backends whose health-check config is unchanged continue probing without interruption.
SIGTERM / SIGINT	Graceful shutdown. Active gRPC streams are closed, the server drains, then the process exits.

Capabilities

maglevd requires CAP_NET_RAW when any health check uses type: icmp. All other check types (tcp, http) use normal TCP sockets and require no special capabilities.

Logging

All log output is written to stdout as JSON using Go's log/slog. The first line logged after the logger is configured is a starting record that includes version, commit, and date. Every state change emits a backend-transition line at INFO level. Set --log-level debug to see individual probe attempts and their outcomes.

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maglevc

maglevc is the interactive control-plane client. It connects to a running maglevd over gRPC and either executes a single command or drops into an interactive shell.

Usage

maglevc [--server host:port] [--color[=bool]] [command...]

Flag	Default	Description
--server	localhost:9090	Address of the maglevd gRPC server.
--color	true	Colorize static field labels in output (dark blue ANSI). Pass --color=false to disable, e.g. when piping.

When command arguments are supplied the command is executed and maglevc exits. When no arguments are given an interactive shell is started and the build version is printed on entry.

Commands

show version                     Print build version, commit hash, and build date.

show frontends                   List all frontend names.
show frontend <name>             Show address, protocol, port, description, and pools.
                                 Each pool lists its backends with weights (if != 100)
                                 and marks disabled backends with [disabled].

show backends                    List all backend names.
show backend <name>              Show address, current state (with duration in that state),
                                 enabled flag, health check, and recent state transitions
                                 with timestamps and how long ago each occurred.

show healthchecks                List all health-check names.
show healthcheck <name>          Show full health-check configuration.

set backend <name> pause         Suspend health checking for a backend, freezing its state.
set backend <name> resume        Resume health checking; backend re-enters unknown state
                                 and is probed immediately.
set frontend <name> pool <pool> backend <name> weight <0-100>
                                 Set the weight of a backend within a pool. Weight 0 keeps
                                 the backend in the pool but assigns it no traffic.
                                 Takes effect immediately without reloading configuration.

set backend <name> disable       Stop probing entirely and remove the backend from rotation.
                                 The backend remains visible (state: removed) and can be
                                 re-enabled without reloading configuration.
set backend <name> enable        Re-enable a disabled backend. A fresh probe goroutine is
                                 started and the backend re-enters unknown state.

watch events                     Stream all events (log, backend transitions, frontend)
  [num <n>]                      Stop after receiving n events.
  [log [level <level>]]          Include log events. level is debug|info|warn|error
                                 (default: info). Omitting log/backend/frontend enables all.
  [backend]                      Include backend transition events.
  [frontend]                     Include frontend events (reserved for future use).

                                 Each event is printed as compact JSON on its own line.
                                 Press any key or Ctrl-C to stop. Examples:

                                   watch events
                                   watch events num 20
                                   watch events log level debug
                                   watch events backend num 100
                                   watch events log level debug backend

config check                     Ask maglevd to read and validate its current config file.
                                 Prints "config ok" on success, or the error (parse or
                                 semantic) returned by the daemon.

quit / exit                      Leave the interactive shell.

Interactive shell

The shell prompt is maglev> . Two completion mechanisms are available:

Tab completion — pressing <Tab> at any point completes the current token. Fixed keywords (commands and subcommands) are completed from the command tree. Backend, frontend, and health-check names are fetched live from the server with a 1-second timeout. If the partial token is unambiguous the word is completed in place; if multiple candidates exist they are listed and the prompt is restored.

Inline help (?) — typing ? at any point prints the available completions for the current position, with a short description next to each keyword. The ? character is not added to the input line.

Commands and keywords support prefix matching: typing sh b is equivalent to show backend provided the prefix is unambiguous. Exact matches always take priority over prefix matches, so show backend and show backends are unambiguous even though one is a prefix of the other.

Command tree and parser

Commands form a tree of Node values. Each node has a fixed Word (a keyword) or is a slot node (marked by a Dynamic function that enumerates valid values at completion time). The parser (Walk) descends the tree token by token:

1. Try to match the current token against the fixed-keyword children of the current node (exact match first, then unique prefix match).
2. If no fixed child matches, try a slot child — any token is accepted and stored as an argument.
3. Stop when tokens are exhausted or no match is found.

The leaf node reached by Walk must have a Run function; otherwise the available sub-commands at that position are printed as help. Arguments collected from slot nodes are passed to Run as a slice.

Example walk for set backend nginx0-ams pause:

root → set → backend → <name>(nginx0-ams collected as arg) → pause

pause.Run is called with args = ["nginx0-ams"].