106 lines
3.5 KiB
Go
106 lines
3.5 KiB
Go
// Package exec is used to invoke child processes across various platforms to
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// provide the following features:
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//
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// - Least privilege
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// - Resource constraints
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// - Process isolation
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//
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// A "platform" may be defined as coarsely as "Windows" or as specifically as
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// "linux 3.20 with systemd". This allows Nomad to use best-effort, best-
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// available capabilities of each platform to provide resource constraints,
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// process isolation, and security features, or otherwise take advantage of
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// features that are unique to that platform.
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//
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// The `semantics of any particular instance are left up to the implementation.
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// However, these should be completely transparent to the calling context. In
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// other words, the Java driver should be able to call exec for any platform and
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// just work.
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package executor
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import (
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"os/exec"
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"path/filepath"
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"github.com/hashicorp/nomad/nomad/structs"
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)
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// Executor is an interface that any platform- or capability-specific exec
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// wrapper must implement. You should not need to implement a Java executor.
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// Rather, you would implement a cgroups executor that the Java driver will use.
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type Executor interface {
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// Limit must be called before Start and restricts the amount of resources
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// the process can use. Note that an error may be returned ONLY IF the
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// executor implements resource limiting. Otherwise Limit is ignored.
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Limit(*structs.Resources) error
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// Start the process. This may wrap the actual process in another command,
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// depending on the capabilities in this environment. Errors that arise from
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// Limits or Runas may bubble through Start()
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Start() error
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// Open should be called to restore a previous execution. This might be needed if
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// nomad is restarted.
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Open(string) error
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// Wait waits till the user's command is completed.
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Wait() error
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// Returns a handle that is executor specific for use in reopening.
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ID() (string, error)
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// Shutdown should use a graceful stop mechanism so the application can
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// perform checkpointing or cleanup, if such a mechanism is available.
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// If such a mechanism is not available, Shutdown() should call ForceStop().
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Shutdown() error
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// ForceStop will terminate the process without waiting for cleanup. Every
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// implementations must provide this.
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ForceStop() error
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// Command provides access the underlying Cmd struct in case the Executor
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// interface doesn't expose the functionality you need.
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Command() *cmd
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}
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// Command is a mirror of exec.Command that returns a platform-specific Executor
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func Command(name string, arg ...string) Executor {
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executor := NewExecutor()
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cmd := executor.Command()
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cmd.Path = name
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cmd.Args = append([]string{name}, arg...)
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if filepath.Base(name) == name {
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if lp, err := exec.LookPath(name); err != nil {
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// cmd.lookPathErr = err
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} else {
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cmd.Path = lp
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}
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}
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return executor
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}
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// OpenId is similar to executor.Command but will attempt to reopen with the
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// passed ID.
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func OpenId(id string) (Executor, error) {
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executor := NewExecutor()
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err := executor.Open(id)
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if err != nil {
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return nil, err
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}
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return executor, nil
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}
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// Cmd is an extension of exec.Cmd that incorporates functionality for
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// re-attaching to processes, dropping priviledges, etc., based on platform-
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// specific implementations.
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type cmd struct {
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exec.Cmd
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// Resources is used to limit CPU and RAM used by the process, by way of
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// cgroups or a similar mechanism.
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Resources structs.Resources
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// RunAs may be a username or Uid. The implementation will decide how to use it.
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RunAs string
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}
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