Go Academy · Lesson

Alternatives: HashiCorp go-plugin

RPC-based plugins for cross-platform support

Lesson 4 of 414 steps

Alternatives: HashiCorp go-plugin is a free Go Academy lesson on CoddyKit. This is lesson 4 of 4. Any 3 lessons of this learning path are free to read in full — after that, CoddyKit PRO unlocks every lesson, plus hands-on practice with a built-in code editor and a 24/7 AI tutor. It is part of the Go Academy learning path, and your progress syncs across the web and the CoddyKit app. The Go Academy course includes 4 lessons in total.

Why go-plugin?

The native Go plugin package is Linux/macOS only, requires identical dependency versions, and cannot unload plugins. HashiCorp go-plugin solves these problems by running plugins as separate processes communicating via RPC (gRPC or net/rpc).

Architecture

go-plugin runs the plugin binary as a subprocess. The host starts it, establishes a gRPC/net/rpc connection, and calls the plugin through a generated client. The plugin process is killed on host exit.

Defining the interface

Define the interface in a shared package, then provide a gRPC or net/rpc bridge.

// shared/interface.go
type Greeter interface {
    Greet(name string) (string, error)
}

Plugin side

The plugin implements the interface and registers it with go-plugin's serve mechanism:

func main() {
    plugin.Serve(&plugin.ServeConfig{
        HandshakeConfig: Handshake,
        Plugins: map[string]plugin.Plugin{
            "greeter": &GreeterPlugin{Impl: &Greeter{}},
        },
        GRPCServer: plugin.DefaultGRPCServer,
    })
}

Host side

The host launches the plugin subprocess and acquires the interface via a client:

client := plugin.NewClient(&plugin.ClientConfig{
    HandshakeConfig: Handshake,
    Plugins:         PluginMap,
    Cmd:             exec.Command("./greeter-plugin"),
    AllowedProtocols: []plugin.Protocol{plugin.ProtocolGRPC},
})
rpcClient, _ := client.Client()
raw, _ := rpcClient.Dispense("greeter")
greeter := raw.(Greeter)

Handshake config

A shared HandshakeConfig (magic cookie key+value) prevents a non-plugin binary from accidentally being launched as a plugin:

var Handshake = plugin.HandshakeConfig{
    ProtocolVersion:  1,
    MagicCookieKey:   "GREETER_PLUGIN",
    MagicCookieValue: "hello",
}

Cross-platform

Because the plugin is a separate process communicating via TCP or Unix socket, it can be compiled for any platform. The host and plugin do not need identical Go versions.

Crash isolation

If a plugin crashes, the host receives an error on the next RPC call. The host can restart the plugin subprocess and reconnect without crashing itself.

Performance

go-plugin RPC adds latency compared to in-process function calls (microseconds vs nanoseconds). Acceptable for infrequent, heavyweight plugin calls; not suitable for hot loops.

Versioning

go-plugin supports protocol versioning — the host can negotiate with multiple versions of a plugin interface simultaneously, enabling gradual plugin upgrades.

Real-world usage

go-plugin powers HashiCorp Terraform providers, Vault secrets engines, and Packer builders — large ecosystems with community-developed plugins.

When to choose

Choose go-plugin over native plugins when: cross-platform support is needed, crash isolation is important, dependency versions cannot be aligned, or plugins are written by third parties.

Quick Check

How does HashiCorp go-plugin achieve crash isolation?

Answer it in the interactive lesson

Recap: HashiCorp go-plugin

Key points:

Plugins run as subprocesses; communicate via gRPC or net/rpc
Cross-platform, crash-isolated, version-tolerant
HandshakeConfig prevents accidental binary launching
Performance overhead from RPC; use for heavyweight/infrequent calls

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