open-nomad/client/logmon/z_logmon_cmd.go

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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
2019-05-13 15:59:52 +00:00
package logmon
import (
"os"
hclog "github.com/hashicorp/go-hclog"
plugin "github.com/hashicorp/go-plugin"
"github.com/hashicorp/nomad/plugins/base"
)
// Install a plugin cli handler to ease working with tests
// and external plugins.
// This init() must be initialized last in package required by the child plugin
// process. It's recommended to avoid any other `init()` or inline any necessary calls
// here. See eeaa95d commit message for more details.
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
2019-05-13 15:59:52 +00:00
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)
}
}