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Use init to handle plugin invocation
Currently, nomad "plugin" processes (e.g. executor, logmon, docker_logger) are started as CLI commands to be handled by command CLI framework. Plugin launchers use `discover.NomadBinary()` to identify the binary and start it. This has few downsides: The trivial one is that when running tests, one must re-compile the nomad binary as the tests need to invoke the nomad executable to start plugin. This is frequently overlooked, resulting in puzzlement. The more significant issue with `executor` in particular is in relation to external driver: * Plugin must identify the path of invoking nomad binary, which is not trivial; `discvoer.NomadBinary()` now returns the path to the plugin rather than to nomad, preventing external drivers from launching executors. * The external driver may get a different version of executor than it expects (specially if we make a binary incompatible change in future). This commit addresses both downside by having the plugin invocation handling through an `init()` call, similar to how libcontainer init handler is done in [1] and recommened by libcontainer [2]. `init()` will be invoked and handled properly in tests and external drivers. For external drivers, this change will cause external drivers to launch the executor that's compiled against. There a are a couple of downsides to this approach: * These specific packages (i.e executor, logmon, and dockerlog) need to be careful in use of `init()`, package initializers. Must avoid having command execution rely on any other init in the package. I prefixed files with `z_` (golang processes files in lexical order), but ensured we don't depend on order. * The command handling is spread in multiple packages making it a bit less obvious how plugin starts are handled. [1] drivers/shared/executor/libcontainer_nsenter_linux.go [2] https://github.com/opencontainers/runc/tree/eb4aeed24ffbf8e2d740fafea39d91faa0ee84d0/libcontainer#using-libcontainer
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Mahmood Ali
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Jun 13, 2019
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,28 @@ | ||
| package logmon | ||
|
|
||
| import ( | ||
| "os" | ||
|
|
||
| hclog "github.com/hashicorp/go-hclog" | ||
| plugin "github.com/hashicorp/go-plugin" | ||
| "github.com/hashicorp/nomad/plugins/base" | ||
| ) | ||
|
|
||
| func init() { | ||
| if len(os.Args) > 1 && os.Args[1] == "logmon" { | ||
| logger := hclog.New(&hclog.LoggerOptions{ | ||
| Level: hclog.Trace, | ||
| JSONFormat: true, | ||
| Name: "logmon", | ||
| }) | ||
| plugin.Serve(&plugin.ServeConfig{ | ||
| HandshakeConfig: base.Handshake, | ||
| Plugins: map[string]plugin.Plugin{ | ||
| "logmon": NewPlugin(NewLogMon(logger)), | ||
| }, | ||
| GRPCServer: plugin.DefaultGRPCServer, | ||
| Logger: logger, | ||
| }) | ||
| os.Exit(0) | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,29 @@ | ||
| package docklog | ||
|
|
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| import ( | ||
| "os" | ||
|
|
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| log "github.com/hashicorp/go-hclog" | ||
| plugin "github.com/hashicorp/go-plugin" | ||
| "github.com/hashicorp/nomad/plugins/base" | ||
| ) | ||
|
|
||
| func init() { | ||
| if len(os.Args) > 1 && os.Args[1] == PluginName { | ||
| logger := log.New(&log.LoggerOptions{ | ||
| Level: log.Trace, | ||
| JSONFormat: true, | ||
| Name: PluginName, | ||
| }) | ||
|
|
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| plugin.Serve(&plugin.ServeConfig{ | ||
| HandshakeConfig: base.Handshake, | ||
| Plugins: map[string]plugin.Plugin{ | ||
| PluginName: NewPlugin(NewDockerLogger(logger)), | ||
| }, | ||
| GRPCServer: plugin.DefaultGRPCServer, | ||
| Logger: logger, | ||
| }) | ||
| os.Exit(0) | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,51 @@ | ||
| package executor | ||
|
|
||
| import ( | ||
| "encoding/json" | ||
| "os" | ||
|
|
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| hclog "github.com/hashicorp/go-hclog" | ||
| log "github.com/hashicorp/go-hclog" | ||
| plugin "github.com/hashicorp/go-plugin" | ||
|
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| "github.com/hashicorp/nomad/plugins/base" | ||
| ) | ||
|
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| func init() { | ||
| if len(os.Args) > 1 && os.Args[1] == "executor" { | ||
| if len(os.Args) != 3 { | ||
| hclog.L().Error("json configuration not provided") | ||
| os.Exit(1) | ||
| } | ||
|
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| config := os.Args[2] | ||
| var executorConfig ExecutorConfig | ||
| if err := json.Unmarshal([]byte(config), &executorConfig); err != nil { | ||
| os.Exit(1) | ||
| } | ||
|
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| f, err := os.OpenFile(executorConfig.LogFile, os.O_CREATE|os.O_RDWR|os.O_APPEND, 0666) | ||
| if err != nil { | ||
| hclog.L().Error(err.Error()) | ||
| os.Exit(1) | ||
| } | ||
|
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| // Create the logger | ||
| logger := log.New(&log.LoggerOptions{ | ||
| Level: hclog.LevelFromString(executorConfig.LogLevel), | ||
| JSONFormat: true, | ||
| Output: f, | ||
| }) | ||
|
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| plugin.Serve(&plugin.ServeConfig{ | ||
| HandshakeConfig: base.Handshake, | ||
| Plugins: GetPluginMap( | ||
| logger, | ||
| executorConfig.FSIsolation, | ||
| ), | ||
| GRPCServer: plugin.DefaultGRPCServer, | ||
| Logger: logger, | ||
| }) | ||
| os.Exit(0) | ||
| } | ||
| } |