Authors: The Yunikorn Scheduler Authors
To define a standard interface that can be used by different types of resource management systems such as YARN/K8s.
- Interface and implementation should be resource manager (RM) agnostic.
- Interface can handle multiple types of resource managers from multiple zones, and different policies can be configured in different zones.
Possible use cases:
- A large cluster needs multiple schedulers to achieve horizontally scalability.
- Multiple resource managers need to run on the same cluster. The managers grow and shrink according to runtime resource usage and policies.
- Handle process-specific information: Scheduler Interface only handles decisions for scheduling instead of how containers will be launched.
Highlights:
- The scheduler should be as stateless as possible. It should try to eliminate any local persistent storage for scheduling decisions.
- When a RM starts, restarts or recovers the RM needs to sync its state with scheduler.
Interface and messages generic definition.
The syntax used for the declarations is proto3. The definition currently only provides go related info.
syntax = "proto3";
package si.v1;
import "google/protobuf/descriptor.proto";
option go_package = "lib/go/si";
extend google.protobuf.FieldOptions {
// Indicates that a field MAY contain information that is sensitive
// and MUST be treated as such (e.g. not logged).
bool si_secret = 1059;
}There are two kinds of interfaces, the first one is RPC based communication, the second one is API based.
RPC based, the gRPC framework is used, will be useful when scheduler has to be deployed as a remote process. For example when we need to deploy scheduler support multiple remote clusters. A second example is when there is a cross language integration, like between Java and Go.
Unless specifically required we strongly recommend the use of the API based interface to avoid the overhead of the RPC serialization and de-serialization.
There are three sets of RPCs:
- Scheduler Service: RM can communicate with the Scheduler Service and do resource allocation/request update, etc.
- Admin Service: Admin can communicate with Scheduler Interface and get configuration updated.
- Metrics Service: Used to retrieve state of scheduler by users / RMs.
Currently only the design and implementation for the Scheduler Service is provided.
service Scheduler {
// Register a RM, if it is a reconnect from previous RM the call will
// trigger a cleanup of all in-memory data and resync with RM.
rpc RegisterResourceManager (RegisterResourceManagerRequest)
returns (RegisterResourceManagerResponse) { }
// Update Scheduler status (this includes node status update, allocation request
// updates, etc. And receive updates from scheduler for allocation changes,
// any required status changes, etc.
// Update allocation request
rpc UpdateAllocation(stream AllocationRequest)
returns (stream AllocationResponse) { }
// Update application request
rpc UpdateApplication(stream ApplicationRequest)
returns (stream ApplicationResponse) { }
// Update node info
rpc UpdateNode(stream NodeRequest)
returns (stream NodeResponse) { }
}The reason of using bi-directional streaming gRPC is, according to performance benchmark: https://grpc.io/docs/guides/benchmarking.html latency is close to 0.5 ms. The same performance benchmark shows streaming QPS can be 4x of non-streaming RPC. Considering scheduler needs both throughput and better latency, we go with streaming API for scheduler related decisions.
The API interface only relies on the message definition and not on other generated code as the RPC Interface does. Below is an example of the Scheduler Service as defined in the RPC. The SchedulerAPI is bi-directional and can be a-synchronous. For the asynchronous cases the API requires a callback interface to be implemented in the resource manager. The callback must be provided to the scheduler as part of the registration.
package api
import "github.com/apache/yunikorn-scheduler-interface/lib/go/si"
type SchedulerAPI interface {
// Register a new RM, if it is a reconnect from previous RM, cleanup
// all in-memory data and resync with RM.
RegisterResourceManager(request *si.RegisterResourceManagerRequest, callback ResourceManagerCallback) (*si.RegisterResourceManagerResponse, error)
// Update allocation request
UpdateAllocation(request *si.AllocationRequest) error
// Update application request
UpdateApplication(request *si.ApplicationRequest) error
// Update node info
UpdateNode(request *si.NodeRequest) error
// Notify scheduler to reload configuration and hot-refresh in-memory state based on configuration changes
UpdateConfiguration(request *si.UpdateConfigurationRequest) error
// Stops the scheduler API service
Stop()
}
// RM side needs to implement this API
type ResourceManagerCallback interface {
//Receive Allocation Update Response
UpdateAllocation(response *si.AllocationResponse) error
//Receive Application Update Response
UpdateApplication(response *si.ApplicationResponse) error
//Receive Node Update Response
UpdateNode(response *si.NodeResponse) error
// Run a certain set of predicate functions to determine if a proposed allocation
// can be allocated onto a node.
Predicates(args *si.PredicatesArgs) error
// Run predicate functions to determine if a proposed allocation can be allocated
// onto a node after preemption. The request contains a list of allocations to
// speculatively remove.
PreemptionPredicates(args *si.PreemptionPredicatesArgs) *si.PreemptionPredicatesResponse
// This plugin is responsible for transmitting events to the shim side.
// Events can be further exposed from the shim.
SendEvent(events []*si.EventRecord)
// Scheduler core can update container scheduling state to the RM,
// the shim side can determine what to do incorporate with the scheduling state
// update container scheduling state to the shim side
// this might be called even the container scheduling state is unchanged
// the shim side cannot assume to only receive updates on state changes
// the shim side implementation must be thread safe
UpdateContainerSchedulingState(request *si.UpdateContainerSchedulingStateRequest)
}
// RM can additionally implement this API to provide information during state dumps
type StateDumpPlugin interface {
// This plugin is responsible for returning a JSON representation of the state of the shim
GetStateDump() (string, error)
}Lifecycle of RM-Scheduler communication
Status of RM in scheduler:
Connection timeout
+-------+ +-------+ loss +-------+ +---------+
|init |+---->|Running|+---->|Paused |+---->| Stopped |
+-------+ +----+--+ +-------+ +---------+
RM register | ^
with scheduler | |
+-----------------------------+
RM voluntarilly
Shutdown
When a new RM starts, fails, it will register with scheduler. In some cases, scheduler can ask RM to re-register because of connection issues or other internal issues.
message RegisterResourceManagerRequest {
// An ID which can uniquely identify a RM **cluster**. (For example, if a RM cluster has multiple manager instances for HA purpose, they should use the same information when do registration).
// If RM register with the same ID, all previous scheduling state in memory will be cleaned up, and expect RM report full scheduling state after registration.
string rmID = 1;
// Version of RM scheduler interface client.
string version = 2;
// Policy group name:
// This defines which policy to use. Policy should be statically configured. (Think about network security group concept of ec2).
// Different RMs can refer to the same policyGroup if their static configuration is identical.
string policyGroup = 3;
// Pass the build information of k8shim to core.
map<string, string> buildInfo = 4;
// Pass the serialized configuration for this policyGroup to core.
string config = 5;
// Additional configuration key/value pairs for configuration not related to the policyGroup.
map<string, string> extraConfig = 6;
}
// Upon success, scheduler returns RegisterResourceManagerResponse to RM, otherwise RM receives exception.
message RegisterResourceManagerResponse {
// Intentionally empty.
}Below is overview of how scheduler/RM keep connection and updates.
message AllocationRequest {
// Allocations can be released.
AllocationReleasesRequest releases = 2;
// ID of RM, this will be used to identify which RM of the request comes from.
string rmID = 3;
// Allocation to add or update.
repeated Allocation allocations = 4;
reserved 1;
reserved "asks";
}
message ApplicationRequest {
// RM should explicitly add application when allocation request also explictly belongs to application.
// This is optional if allocation request doesn't belong to a application. (Independent allocation)
repeated AddApplicationRequest new = 1;
// RM can also remove applications, all allocation/allocation requests associated with the application will be removed
repeated RemoveApplicationRequest remove = 2;
// ID of RM, this will be used to identify which RM of the request comes from.
string rmID = 3;
}
message NodeRequest {
// New node can be scheduled. If a node is notified to be "unscheduable", it needs to be part of this field as well.
repeated NodeInfo nodes = 1;
// ID of RM, this will be used to identify which RM of the request comes from.
string rmID = 2;
}
message AllocationResponse {
// New allocations
repeated Allocation new = 1;
// Released allocations, this could be either ack from scheduler when RM asks to terminate some allocations.
// Or it could be decision made by scheduler (such as preemption or timeout).
repeated AllocationRelease released = 2;
// Rejected allocations
repeated RejectedAllocation rejectedAllocations = 5;
reserved 3;
reserved "releasedAsks";
reserved 4;
reserved "rejected";
}
message ApplicationResponse {
// Rejected Applications
repeated RejectedApplication rejected = 1;
// Accepted Applications
repeated AcceptedApplication accepted = 2;
// Updated Applications
repeated UpdatedApplication updated = 3;
}
message NodeResponse {
// Rejected Node Registrations
repeated RejectedNode rejected = 1;
// Accepted Node Registrations
repeated AcceptedNode accepted = 2;
}
message UpdatedApplication {
// The application ID that was updated
string applicationID = 1;
// State of the application
string state = 2;
// Timestamp of the state transition
int64 stateTransitionTimestamp = 3;
// Detailed message
string message = 4;
}
message RejectedApplication {
// The application ID that was rejected
string applicationID = 1;
// A human-readable reason message
string reason = 2;
}
message AcceptedApplication {
// The application ID that was accepted
string applicationID = 1;
}
message RejectedNode {
// The node ID that was rejected
string nodeID = 1;
// A human-readable reason message
string reason = 2;
}
message AcceptedNode {
// The node ID that was accepted
string nodeID = 1;
}Lifecycle of Allocation:
Rejected by Scheduler
+-------------------------------------------+
| |
| v
+-------+---+ Asked +-----------+Scheduler or,+-----------+
| Initial |+------>|Pending |+----+----+->|Rejected |
+-----------+ By RM +-----+-----+ Asked by RM +-----------+
|
v
+-----------+ +------------+
|Allocated |+-------+|Completed |
+---+-------+ Stopped +------------+
| by RM
| +------------+
+--------------->|Preempted |
+ Preempted by +------------+
| Scheduler
| +------------+
+--------------->|Expired |
Timeout +------------+
(Part of Allocation request)
Common fields for allocation:
// A sparse map of resource to Quantity.
message Resource {
map<string, Quantity> resources = 1;
}
// Quantity includes a single int64 value
message Quantity {
int64 value = 1;
}Preemption policy:
message PreemptionPolicy {
// Opt-out from preemption
bool allowPreemptSelf = 1;
// Allow preemption of other tasks with same or lower priority
bool allowPreemptOther = 2;
}Application requests:
message AddApplicationRequest {
// The ID of the application, must be unique
string applicationID = 1;
// The queue this application is requesting. The scheduler will place the application into a
// queue according to policy, taking into account the requested queue as per the policy.
string queueName = 2;
// The partition the application belongs to
string partitionName = 3;
// The user group information of the application owner
UserGroupInformation ugi = 4;
// A set of tags for the application. These tags provide application level generic information.
// The tags are optional and are used in placing an application or scheduling.
map<string, string> tags = 5;
// Execution timeout: How long this application can be in a running state
// 0 or negative value means never expire.
int64 executionTimeoutMilliSeconds = 6;
// The total amount of resources gang placeholders will request
Resource placeholderAsk = 7;
// Gang scheduling style can be hard (the application will fail after placeholder timeout)
// or soft (after the timeout the application will be scheduled as a normal application)
string gangSchedulingStyle = 8;
}
message RemoveApplicationRequest {
// The ID of the application to remove
string applicationID = 1;
// The partition the application belongs to
string partitionName = 2;
}User information: The user that owns the application. Group information can be empty. If the group information is empty the groups will be resolved by the scheduler when needed.
message UserGroupInformation {
// the user name
string user = 1;
// the list of groups of the user, can be empty
repeated string groups = 2;
}The Allocation message is used in two cases:
- A recovered allocation send from the RM to the scheduler
- A newly created allocation from the scheduler.
message Allocation {
// Allocation key
string allocationKey = 1;
// Allocation tags
map<string, string> allocationTags = 2;
// Resource for each allocation
Resource resourcePerAlloc = 5;
// Priority of allocation
int32 priority = 6;
// Node which the allocation belongs to
string nodeID = 8;
// The ID of the application
string applicationID = 9;
// Partition of the allocation
string partitionName = 10;
// The name of the TaskGroup this allocation belongs to
string taskGroupName = 11;
// Is this a placeholder allocation (true) or a real allocation (false), defaults to false
// ignored if the taskGroupName is not set
bool placeholder = 12;
// Whether this allocation was the originator of this app
bool originator = 14;
// The preemption policy for this allocation
PreemptionPolicy preemptionPolicy = 15;
reserved 7;
reserved "queueName";
reserved 3;
reserved "UUID";
reserved 13;
reserved "allocationID";
}message AllocationReleasesRequest {
// The allocations to release
repeated AllocationRelease allocationsToRelease = 1;
reserved 2;
reserved "allocationAsksToRelease";
}
enum TerminationType {
UNKNOWN_TERMINATION_TYPE = 0;//TerminationType not set
STOPPED_BY_RM = 1; // Stopped or killed by ResourceManager (created by RM)
TIMEOUT = 2; // Timed out based on the executionTimeoutMilliSeconds (created by core)
PREEMPTED_BY_SCHEDULER = 3; // Preempted allocation by scheduler (created by core)
PLACEHOLDER_REPLACED = 4; // Placeholder allocation replaced by real allocation (created by core)
}
// Release allocation: this is a bidirectional message. The Terminationtype defines the origin, or creator,
// as per the comment. The confirmation or response from the receiver is the same message with the same
// termination type set.
message AllocationRelease {
// The name of the partition the allocation belongs to
string partitionName = 1;
// The application the allocation belongs to
string applicationID = 2;
// Termination type of the released allocation
TerminationType terminationType = 4;
// human-readable message
string message = 5;
// AllocationKey of the allocation to release, if not set all allocations are released for the applicationID
string allocationKey = 6;
reserved 3;
reserved "UUID";
reserved 7;
reserved "allocationID";
}State transition of node:
+-----------+ +--------+ +-------+
|SCHEDULABLE|+-------->|DRAINING|+---------->|REMOVED|
+-----------+ +--------+ +-------+
^ Asked by + Asked by
| RM to DRAIN | RM to REMOVE
| |
+---------------------+
Asked by RM to
SCHEDULE again
See protocol below:
During new node registration with the scheduler, request will be rejected if the node exist already. While updating registered node with the scheduler, request will fail if the node doesn't exist.
message NodeInfo {
// Action from RM
enum ActionFromRM {
//ActionFromRM not set
UNKNOWN_ACTION_FROM_RM = 0;
// Create Node as initially schedulable.
CREATE = 1;
// Update node resources, attributes.
UPDATE = 2;
// Do not allocate new allocations on the node.
DRAIN_NODE = 3;
// Decomission node, it will immediately stop allocations on the node and
// remove the node from schedulable lists.
DECOMISSION = 4;
// From Draining state to SCHEDULABLE state.
// If node is not in draining state, error will be thrown
DRAIN_TO_SCHEDULABLE = 5;
// Create Node as initially draining (i.e. unschedulable). Before scheduling can proceed,
// DRAIN_TO_SCHEDULABLE must be called.
CREATE_DRAIN = 6;
}
// ID of node, the node must exist to be updated
string nodeID = 1;
// Action to perform by the scheduler
ActionFromRM action = 2;
// New attributes of node, which will replace previously reported attribute.
map<string, string> attributes = 3;
// new schedulable resource, scheduler may preempt allocations on the
// node or schedule more allocations accordingly.
Resource schedulableResource = 4;
// when the scheduler is co-exist with some other schedulers, some node
// resources might be occupied (allocated) by other schedulers.
Resource occupiedResource = 5;
reserved 6;
reserved "existingAllocations";
}The following is the feedback produced from the scheduler to the RM:
Rejected allocation:
message RejectedAllocation {
// the ID of the allocation
string allocationKey = 1;
// The ID of the application
string applicationID = 2;
// A human-readable reason message
string reason = 3;
}Scheduler Interface attributes start with the si prefix. Such constants are for example known attribute names for nodes and applications.
// Constants for node attributes
const (
ARCH = "si/arch"
HostName = "si/hostname"
RackName = "si/rackname"
OS = "si/os"
InstanceType = "si/instance-type"
FailureDomainZone = "si/zone"
FailureDomainRegion = "si/region"
LocalImages = "si/local-images"
NodePartition = "si/node-partition"
)
// Constants for allocation attributes
const (
ApplicationID = "si/application-id"
ContainerImage = "si/container-image"
ContainerPorts = "si/container-ports"
)
Allocation tags are key-value pairs, where the key should contain a domain, and optionally a group part.
These parts should precede the name of the key (and should be in that order) and separated by a "/" character.
Example allocation key: kubernetes.io/meta/namespace.
// Constants for allocation tags
const (
// Domains
DomainK8s = "kubernetes.io/"
DomainYuniKorn = "yunikorn.apache.org/"
DomainYuniKornInternal = "internal.yunikorn.apache.org/"
// Groups
GroupMeta = "meta/"
GroupLabel = "label/"
GroupAnnotation = "annotation/"
// Keys
KeyPodName = "podName"
KeyNamespace = "namespace"
KeyRequiredNode = "requiredNode"
// Pods
CreationTime = "creationTime"
Foreign = "foreign"
AllocTypeStatic = "static"
AllocTypeDefault = "default"
)
Miscellaneous constants for resources and other values.
// Constants for Core and Shim
const (
Memory = "memory"
CPU = "vcore"
AppTagNamespaceResourceQuota = "namespace.resourcequota"
AppTagNamespaceResourceGuaranteed = "namespace.resourceguaranteed"
AppTagNamespaceResourceMaxApps = "namespace.resourcemaxapps"
AppTagCreateForce = "application.create.force"
)
SchedulerPlugin is a way to extend scheduler capabilities. Scheduler shim can implement such plugin and register itself to yunikorn-core, so plugged function can be invoked in the scheduler core.
message PredicatesArgs {
// allocation key identifies a container, the predicates function is going to check
// if this container is eligible to be placed ont to a node.
string allocationKey = 1;
// the node ID the container is assigned to.
string nodeID = 2;
// run the predicates for alloactions (true) or reservations (false)
bool allocate = 3;
}
message PreemptionPredicatesArgs {
// the allocation key of the container to check
string allocationKey = 1;
// the node ID the container should be attempted to be scheduled on
string nodeID = 2;
// a list of existing allocations that should be tentatively removed before checking
repeated string preemptAllocationKeys = 3;
// index of last allocation in starting attempt (first attempt should be 0..startIndex)
int32 startIndex = 4;
}
message PreemptionPredicatesResponse {
// whether or not container will schedule on the node
bool success = 1;
// index of last allocation which was removed before success (ignored during failure)
int32 index = 2;
}
message UpdateContainerSchedulingStateRequest {
// container scheduling states
enum SchedulingState {
//SchedulingState not set
UNKNOWN_SCHEDULING_STATE = 0;
// the container is being skipped by the scheduler
SKIPPED = 1;
// the container is scheduled and it has been assigned to a node
SCHEDULED = 2;
// the container is reserved on some node, but not yet assigned
RESERVED = 3;
// scheduler has visited all candidate nodes for this container
// but non of them could satisfy this container's requirement
FAILED = 4;
}
// application ID
string applicationID = 1;
// allocation key used to identify a container.
string allocationKey = 2;
// container scheduling state
SchedulingState state = 3;
// an optional plain message to explain why it is in such state
string reason = 4;
}
message UpdateConfigurationRequest {
// RM ID to update
string rmID = 2;
// PolicyGroup to update
string policyGroup = 3;
// New configuration to update
string config = 4;
// Additional configuration key/value pairs for configuration not related to the policyGroup.
map<string, string> extraConfig = 5;
reserved 1;
reserved "configs";
}The Event Cache is a SchedulerPlugin that exposes events about scheduler objects aiming to help the end user to
see these events from the shim side. An event is sent to the shim through the callback as an EventRecord.
An EventRecord consists of the following fields:
message EventRecord {
enum Type {
//EventRecord Type not set
UNKNOWN_EVENTRECORD_TYPE = 0;
REQUEST = 1;
APP = 2;
NODE = 3;
QUEUE = 4;
USERGROUP = 5;
}
enum ChangeType {
NONE = 0;
SET = 1;
ADD = 2;
REMOVE = 3;
}
enum ChangeDetail {
DETAILS_NONE = 0;
REQUEST_CANCEL = 100; // Request cancelled by the RM
REQUEST_ALLOC = 101; // Request allocated
REQUEST_TIMEOUT = 102; // Request cancelled due to timeout
APP_ALLOC = 200; // Allocation changed
APP_REQUEST = 201; // Request changed
APP_REJECT = 202; // Application rejected on create
APP_NEW = 203; // Application added with state new
APP_ACCEPTED = 204; // State change to accepted
APP_RUNNING = 206; // State change to running
APP_COMPLETING = 207; // State change to completing
APP_COMPLETED = 208; // State change to completed
APP_FAILING = 209; // State change to failing
APP_FAILED = 210; // State change to failed
APP_RESUMING = 211; // State change to resuming
APP_EXPIRED = 212; // State change to expired
APP_CANNOTRUN_QUEUE = 213; // Application cannot run in the queue (maxApplications hit)
APP_RUNNABLE_QUEUE = 214; // Application is allowed to run (after maxApplications limit hit)
APP_CANNOTRUN_QUOTA = 215; // Application cannot run due to user/group quota (maxApplications hit)
APP_RUNNABLE_QUOTA = 216; // Application is allowed to run based on user/group quota (after maxApplications limit hit)
NODE_DECOMISSION = 300; // Node removal
NODE_SCHEDULABLE = 302; // Node schedulable state change (cordon)
NODE_ALLOC = 303; // Allocation changed
NODE_CAPACITY = 304; // Capacity changed
NODE_OCCUPIED = 305; // Occupied resource changed
NODE_RESERVATION = 306; // Reservation/unreservation occurred
QUEUE_CONFIG = 400; // Managed queue update or removal
QUEUE_DYNAMIC = 401; // Dynamic queue update or removal
QUEUE_TYPE = 402; // Queue type change
QUEUE_MAX = 403; // Max resource changed
QUEUE_GUARANTEED = 404; // Guaranteed resource changed
QUEUE_APP = 405; // Application changed
QUEUE_ALLOC = 406; // Allocation changed
ALLOC_CANCEL = 500; // Allocation cancelled by the RM
ALLOC_PREEMPT = 501; // Allocation preempted by the core
ALLOC_TIMEOUT = 502; // Allocation cancelled due to timeout
ALLOC_REPLACED = 503; // Allocation replacement (placeholder)
ALLOC_NODEREMOVED = 504; // Allocation cancelled, node removal
UG_USER_LIMIT = 600; // Limit is changed (set/unset) for a given user
UG_GROUP_LIMIT = 601; // Limit is changed (set/unset) for a given group
UG_APP_LINK = 602; // Linkage is changed (created/removed) between an application and a group
UG_USER_RESOURCE = 603; // Resource usage updated for a user
UG_GROUP_RESOURCE = 604; // Resource usage updated for a group
reserved 205;
reserved 301;
reserved "APP_STARTING";
reserved "NODE_READY";
}
// the type of the object associated with the event
Type type = 1;
// ID of the object associated with the event
string objectID = 2;
// the detailed message as string
string message = 5;
// timestamp of the event
int64 timestampNano = 6;
// the type of the change
ChangeType eventChangeType = 7;
// details about the change
ChangeDetail eventChangeDetail = 8;
// the secondary object in the event (eg. allocation ID, request ID)
string referenceID = 9;
// the resource value if the change involves setting/modifying a resource
Resource resource = 10;
reserved 3;
reserved "groupID";
reserved 4;
reserved "reason";
}