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eeaa95ddf9
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] eb4aeed24f/libcontainer (using-libcontainer)
52 lines
1.1 KiB
Go
52 lines
1.1 KiB
Go
package executor
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import (
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"encoding/json"
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"os"
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hclog "github.com/hashicorp/go-hclog"
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log "github.com/hashicorp/go-hclog"
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plugin "github.com/hashicorp/go-plugin"
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"github.com/hashicorp/nomad/plugins/base"
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)
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func init() {
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if len(os.Args) > 1 && os.Args[1] == "executor" {
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if len(os.Args) != 3 {
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hclog.L().Error("json configuration not provided")
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os.Exit(1)
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}
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config := os.Args[2]
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var executorConfig ExecutorConfig
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if err := json.Unmarshal([]byte(config), &executorConfig); err != nil {
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os.Exit(1)
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}
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f, err := os.OpenFile(executorConfig.LogFile, os.O_CREATE|os.O_RDWR|os.O_APPEND, 0666)
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if err != nil {
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hclog.L().Error(err.Error())
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os.Exit(1)
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}
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// Create the logger
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logger := log.New(&log.LoggerOptions{
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Level: hclog.LevelFromString(executorConfig.LogLevel),
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JSONFormat: true,
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Output: f,
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})
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plugin.Serve(&plugin.ServeConfig{
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HandshakeConfig: base.Handshake,
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Plugins: GetPluginMap(
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logger,
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executorConfig.FSIsolation,
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),
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GRPCServer: plugin.DefaultGRPCServer,
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Logger: logger,
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})
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os.Exit(0)
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}
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}
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