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5da1a31e94
This PR introduces support for using Nomad on systems with cgroups v2 [1] enabled as the cgroups controller mounted on /sys/fs/cgroups. Newer Linux distros like Ubuntu 21.10 are shipping with cgroups v2 only, causing problems for Nomad users. Nomad mostly "just works" with cgroups v2 due to the indirection via libcontainer, but not so for managing cpuset cgroups. Before, Nomad has been making use of a feature in v1 where a PID could be a member of more than one cgroup. In v2 this is no longer possible, and so the logic around computing cpuset values must be modified. When Nomad detects v2, it manages cpuset values in-process, rather than making use of cgroup heirarchy inheritence via shared/reserved parents. Nomad will only activate the v2 logic when it detects cgroups2 is mounted at /sys/fs/cgroups. This means on systems running in hybrid mode with cgroups2 mounted at /sys/fs/cgroups/unified (as is typical) Nomad will continue to use the v1 logic, and should operate as before. Systems that do not support cgroups v2 are also not affected. When v2 is activated, Nomad will create a parent called nomad.slice (unless otherwise configured in Client conifg), and create cgroups for tasks using naming convention <allocID>-<task>.scope. These follow the naming convention set by systemd and also used by Docker when cgroups v2 is detected. Client nodes now export a new fingerprint attribute, unique.cgroups.version which will be set to 'v1' or 'v2' to indicate the cgroups regime in use by Nomad. The new cpuset management strategy fixes #11705, where docker tasks that spawned processes on startup would "leak". In cgroups v2, the PIDs are started in the cgroup they will always live in, and thus the cause of the leak is eliminated. [1] https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html Closes #11289 Fixes #11705 #11773 #11933
88 lines
2.5 KiB
Go
88 lines
2.5 KiB
Go
package cgutil
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import (
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"context"
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"fmt"
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"path/filepath"
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"strings"
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"github.com/hashicorp/nomad/lib/cpuset"
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"github.com/hashicorp/nomad/nomad/structs"
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)
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const (
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// CgroupRoot is hard-coded in the cgroups specification.
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// It only applies to linux but helpers have references to it in driver(s).
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CgroupRoot = "/sys/fs/cgroup"
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)
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// CpusetManager is used to setup cpuset cgroups for each task.
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type CpusetManager interface {
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// Init should be called with the initial set of reservable cores before any
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// allocations are managed. Ensures the parent cgroup exists and proper permissions
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// are available for managing cgroups.
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Init([]uint16) error
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// AddAlloc adds an allocation to the manager
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AddAlloc(alloc *structs.Allocation)
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// RemoveAlloc removes an alloc by ID from the manager
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RemoveAlloc(allocID string)
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// CgroupPathFor returns a callback for getting the cgroup path and any error that may have occurred during
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// cgroup initialization. The callback will block if the cgroup has not been created
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CgroupPathFor(allocID, taskName string) CgroupPathGetter
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}
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type NoopCpusetManager struct{}
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func (n NoopCpusetManager) Init([]uint16) error {
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return nil
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}
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func (n NoopCpusetManager) AddAlloc(alloc *structs.Allocation) {
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}
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func (n NoopCpusetManager) RemoveAlloc(allocID string) {
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}
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func (n NoopCpusetManager) CgroupPathFor(allocID, task string) CgroupPathGetter {
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return func(context.Context) (string, error) { return "", nil }
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}
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// CgroupPathGetter is a function which returns the cgroup path and any error which
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// occurred during cgroup initialization.
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//
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// It should block until the cgroup has been created or an error is reported.
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type CgroupPathGetter func(context.Context) (path string, err error)
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type TaskCgroupInfo struct {
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CgroupPath string
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RelativeCgroupPath string
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Cpuset cpuset.CPUSet
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Error error
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}
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// identity is the "<allocID>.<taskName>" string that uniquely identifies an
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// individual instance of a task within the flat cgroup namespace
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type identity string
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func makeID(allocID, task string) identity {
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return identity(fmt.Sprintf("%s.%s", allocID, task))
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}
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func makeScope(id identity) string {
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return string(id) + ".scope"
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}
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// SplitPath determines the parent and cgroup from p.
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// p must contain at least 2 elements (parent + cgroup).
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//
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// Handles the cgroup root if present.
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func SplitPath(p string) (string, string) {
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p = strings.TrimPrefix(p, CgroupRoot)
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p = strings.Trim(p, "/")
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parts := strings.Split(p, "/")
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return parts[0], "/" + filepath.Join(parts[1:]...)
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}
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