kubecon eu 2016: custom volume plugins

Custom VolumePlugins

@agonzalezro

Just one thing

It's easy!

Easier than you might think

What's a

volume?

Persistentvs

Non persistent

User POV

spec: containers: - name: web image: nginx ports: - name: web containerPort: 80 volumeMounts: - name: www-root mountPath: "/usr/share/nginx/html"

volumes: - name: www-root flocker: datasetName: my-flocker-vol

... volumeMounts: - name: www-root mountPath: "/usr/share/nginx/html"

volumes: - name: www-root flocker: datasetName: my-flocker-vol

Available4 AWS EBS, GCE PD, Azure File

4 Git Repo

4 NFS

4 GlusterFS, Cinder

4 Flocker

4 Secrets

Is this

new?

HTTP API

/VolumeDriver.Create .Mount .Path .Unmount .Remove

Go interface{}

1. Add it to the API (pkg/api/{,v1/}types.go):

type VolumeSource struct { EmptyDir *EmptyDirVolumeSource `json:"emptyDir,omitempty"` Flocker *FlockerVolumeSource `json:"flocker,omitempty"` ...

2. Add it to the Kubelet (cmd/kubelet/app/plugins.go):

func ProbeVolumePlugins(pluginDir string) []volume.VolumePlugin { allPlugins := []volume.VolumePlugin{} allPlugins = append(allPlugins, empty_dir.ProbeVolumePlugins()...) allPlugins = append(allPlugins, git_repo.ProbeVolumePlugins()...) ...

3. Implement the volume plugin (pkg/volume/...):

type VolumePlugin interface { Init(host VolumeHost) error Name() string CanSupport(spec *Spec) bool

NewBuilder(spec *Spec, podRef *api.Pod, opts VolumeOptions) (Builder, error) NewCleaner(name string, podUID types.UID) (Cleaner, error)}

type VolumePlugin interface { Init(host VolumeHost) error Name() string CanSupport(spec *Spec) bool ...

... NewBuilder( spec *Spec, podRef *api.Pod, opts VolumeOptions, ) (Builder, error)

NewCleaner( name string, podUID types.UID, ) (Cleaner, error)}

Simplified example of NewBuilder

func (p *plg) NewBuilder(spec, pod, opts) (volume.Builder, error) { source, _ := p.getFlockerVolumeSource(spec) builder := flockerBuilder{ flocker: &flocker{ datasetName: source.DatasetName, pod: pod, ... }, ... } return &builder, nil}

4. Implement the builder

type Builder interface { Volume

SetUp(fsGroup *int64) error SetUpAt(dir string, fsGroup *int64) error GetAttributes() Attributes}

Simplified example of SetUpAt for git repo

I lied

func (b *gitRepoVolumeBuilder) SetUpAt(dir string, fsGroup *int64) error { if volumeutil.IsReady(b.getMetaDir()) { return nil }

wrapped, err := b.plugin.host.NewWrapperBuilder(b.volName, wrappedVolumeSpec, &b.pod, b.opts) if err != nil { return err } if err := wrapped.SetUpAt(dir, fsGroup); err != nil { return err }

args := []string{"clone", b.source}

if len(b.target) != 0 { args = append(args, b.target) } if output, err := b.execCommand("git", args, dir); err != nil { return fmt.Errorf("failed to exec 'git %s': %s: %v", strings.Join(args, " "), output, err) }

files, err := ioutil.ReadDir(dir) if err != nil { return err }

if len(b.revision) == 0 { // Done! volumeutil.SetReady(b.getMetaDir()) return nil }

var subdir string

switch { case b.target == ".": // if target dir is '.', use the current dir subdir = path.Join(dir) case len(files) == 1: // if target is not '.', use the generated folder subdir = path.Join(dir, files[0].Name()) default: // if target is not '.', but generated many files, it's wrong return fmt.Errorf("unexpected directory contents: %v", files) }

if output, err := b.execCommand("git", []string{"checkout", b.revision}, subdir); err != nil { return fmt.Errorf("failed to exec 'git checkout %s': %s: %v", b.revision, output, err) } if output, err := b.execCommand("git", []string{"reset", "--hard"}, subdir); err != nil { return fmt.Errorf("failed to exec 'git reset --hard': %s: %v", output, err) }

volumeutil.SetReady(b.getMetaDir()) return nil}

1. Check meta: was it called before? Is it ready?

2. Use empty dir to prepare the path

3. git clone it

4. Checkout the revision sent on the pod definition

5. Job done? Mark as ready

Important bit of empty_dir

switch ed.medium { case api.StorageMediumDefault: err = ed.setupDir(dir) case api.StorageMediumMemory: err = ed.setupTmpfs(dir, securityContext) default: err = fmt.Errorf("unknown storage medium %q", ed.medium) }

volume.SetVolumeOwnership(ed, fsGroup)

Another simplified example for Flocker

I liedagain

func (b flockerBuilder) SetUpAt(dir string, fsGroup *int64) error { if volumeutil.IsReady(b.getMetaDir()) { return nil }

if b.client == nil { c, err := b.newFlockerClient() if err != nil { return err } b.client = c }

datasetID, err := b.client.GetDatasetID(dir) if err != nil { return err }

s, err := b.client.GetDatasetState(datasetID) if err != nil { return fmt.Errorf("The volume '%s' is not available in Flocker. You need to create this manually with Flocker CLI before using it.", dir) }

primaryUUID, err := b.client.GetPrimaryUUID() if err != nil { return err }

if s.Primary != primaryUUID { if err := b.updateDatasetPrimary(datasetID, primaryUUID); err != nil { return err } }

b.flocker.path = s.Path volumeutil.SetReady(b.getMetaDir()) return nil}

1. Was it called? Is it ready?

2. Is the dataset ready? If not, not my problem mate

3. If primary UUIDs doesn't match (rescheduled pod), update them

4. Wait until ready

5. Mark as ready

5. Implement the Persistent Volume Plugin

type PersistentVolumePlugin interface { VolumePlugin

GetAccessModes() []api.PersistentVolumeAccessMode}

func (p *plg) GetAccessModes() []api.PersistentVolumeAccessMode { return []api.PersistentVolumeAccessMode{ api.ReadWriteOnce, }}

http://bit.ly/kubecon

"Problems"

4 CLAs

4 Shippable & Jenkins

4 hack/ scripts

4 PR

Summary1. Add API

2. Enable the plugin on the Kubelet

3. Implement VolumePlugin interface: NewBuilder & NewCleaner

4. Implement the builder itself: SetUpAt

5. Persistent?

6. ❤

Just one (more) thing

We are hiring at

Thanks!@agonzalezro