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.
Possible use cases:
Highlights:
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 = "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:
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. rpc Update (stream UpdateRequest) returns (stream UpdateResponse) { } } /* service AdminService { // Include // addQueueInfo. // removeQueueInfo. // updateQueueInfo. // Ref: org.apache.hadoop.yarn.webapp.dao.SchedConfUpdateInfo rpc UpdateConfig (UpdateConfigRequest) returns (UpdateConfigResponse) {} } */ /* service MetricsService { } */
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.infra.cloudera.com/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 Scheduler status (including node status update, allocation request // updates, etc. Update(request *si.UpdateRequest) error } // RM side needs to implement this API type ResourceManagerCallback interface { RecvUpdateResponse(response *si.UpdateResponse) 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; } // 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 UpdateRequest { // New allocation requests or replace existing allocation request (if allocation-id is same) repeated AllocationAsk asks = 1; // Allocations can be released. AllocationReleasesRequest releases = 2; // New node can be scheduled. If a node is notified to be "unscheduable", it needs to be part of this field as well. repeated NewNodeInfo newSchedulableNodes = 3; // Update nodes for existing schedulable nodes. // May include: // - Node resource changes. (Like grows/shrinks node resource) // - Node attribute changes. (Including node-partition concept like YARN, and concept like "local images". // // Should not include: // - Allocation-related changes with the node. // - Realtime Utilizations. repeated UpdateNodeInfo updatedNodes = 4; // UtilizationReports for allocation and nodes. repeated UtilizationReport utilizationReports = 5; // Id of RM, this will be used to identify which RM of the request comes from. string rmId = 6; // 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 newApplications = 8; // RM can also remove applications, all allocation/allocation requests associated with the application will be removed repeated RemoveApplicationRequest removeApplications = 9; } message UpdateResponse { // Scheduler can send action to RM. enum ActionFromScheduler { // Nothing needs to do NOACTION = 0; // Something is wrong, RM needs to stop the RM, and re-register with scheduler. RESYNC = 1; } // What RM needs to do, scheduler can send control code to RM when something goes wrong. // Don't use/expand this field for other general purposed actions. (Like kill a remote container process). ActionFromScheduler action = 1; // New allocations repeated Allocation newAllocations = 2; // 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). repeated AllocationReleaseResponse releasedAllocations = 3; // Rejected allocation requests repeated RejectedAllocationAsk rejectedAllocations = 4; // Suggested node update. // This could include: // 1) Schedulable resources on each node. This can be used when we want to run // two resource management systems side-by-side. For example, YARN/K8s running side by side. // and update YARN NodeManager / Kubelet resource dynamically. // 2) Other recommendations. repeated NodeRecommendation nodeRecommendations = 5; // Rejected Applications repeated RejectedApplication rejectedApplications = 6; // Accepted Applications repeated AcceptedApplication acceptedApplications = 7; // Rejected Node Registrations repeated RejectedNode rejectedNodes = 8; // Accepted Node Registrations repeated AcceptedNode acceptedNodes = 9; } message RejectedApplication { string applicationId = 1; string reason = 2; } message AcceptedApplication { string applicationId = 1; } message RejectedNode { string nodeId = 1; string reason = 2; } message AcceptedNode { string nodeId = 1; }
Lifecycle of AllocationAsk:
Rejected by Scheduler
+-------------------------------------------+
| |
| v
+-------+---+ Asked +-----------+Scheduler or,+-----------+
|Initial +------->|Pending |+----+----+->|Rejected |
+-----------+By RM +-+---------+ Asked by RM +-----------+
+
|
v
+-----------+
|Allocated |
+-----------+
Lifecycle of Allocations:
+--Allocated by
v Scheduler
+-----------+ +------------+
|Allocated |+------ |Completed |
+---+-------+ Stoppe +------------+
| by RM
| +------------+
+--------------->|Preempted |
+ Preempted by +------------+
| Scheduler
|
|
| +------------+
+--------------->|Expired |
Timeout +------------+
(Part of Allocation
ask)
Common fields for allocation:
message Priority { oneof priority { // Priority of each ask, higher is more important. // How to deal with Priority is handled by each scheduler implementation. int32 priorityValue = 1; // PriorityClass is used for app owners to set named priorities. This is a portable way for // app owners have a consistent way to setup priority across clusters string priorityClassName = 2; } } // 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; }
Allocation ask:
message AllocationAsk { // Allocation key is used by both of scheduler and RM to track container allocation. // It doesn't have to be same as RM's internal allocation id (such as Pod name of K8s or ContainerId of YARN). // If multiple allocation from a same AllocationAsk returned to RM, they will share the same allocationKey. // If ALlocationAsk with the same allocationKey exists, old one will be replaced by the new one. string allocationKey = 1; // How much resource per allocation? Resource resourceAsk = 2; // Tags of Allocation map<string, string> tags = 3; // Priority of ask Priority priority = 4; // Placement constraint defines how app wanna to be placed in the cluster. // if not set, no placement constraint will be applied. PlacementConstraint placementConstraint = 6; // Maximum number of allocations int32 maxAllocations = 7; // Who owns the allocation UserGroupInformation ugi = 8; // Place this allocation to specified queue. // If queue not specified, scheduler will place the allocation to a queue // according to policy // When queue is specified and allocation cannot be allocated in asked queue // AllocationAsk will be rejected. string queueName = 9; // Execution timeout: How long this allocation will be terminated (by scheduler) // once allocated by scheduler, 0 or negative value means never expire. int64 executionTimeoutMilliSeconds = 10; // Which application this allocation ask belongs to, if it is not specified. The allocation // won't belong to any application. string applicationId = 11; // Which partition requested by this ask // One ask can only request one node partition string PartitionName = 12; // TODO. // wangda: even if I don't like it, it seems we have to support old-school style // YARN resource requests, otherwise it gonna be very hard to support legacy apps // running on YARN. // Maybe a simple approach is to add a flag to indicate it is an old-school resource // request from YARN. // Check: YARN code: placement.LocalityAppPlacementAllocator for more details. } message UserGroupInformation { string user = 1; repeated string groups = 2; } message AddApplicationRequest { string applicationId = 1; string queueName = 2; string partitionName = 3; } message RemoveApplicationRequest { string applicationId = 1; string partitionName = 2; }
PlacementConstraint: (Reference to works have been done in YARN-6592). And here is design doc: https://issues.apache.org/jira/secure/attachment/12867869/YARN-6592-Rich-Placement-Constraints-Design-V1.pdf
// PlacementConstraint could have simplePlacementConstraint or // CompositePlacementConstraint. One of them will be set. message PlacementConstraint { oneof constraint { SimplePlacementConstraint simpleConstraint = 1; // This protocol can extended to support complex constraints // To make an easier scheduler implementation and avoid confusing user. // Protocol related to CompositePlacementConstraints will be // commented and only for your references. // CompositePlacementConstraint compositeConstraint = 2; } } // Simple placement constraint represent constraint for affinity/anti-affinity // to node attribute or allocation tags. // When both of NodeAffinityConstraints and AllocationAffinityConstraints // specified, both will be checked and verified while scheduling. message SimplePlacementConstraint { // Constraint NodeAffinityConstraints nodeAffinityConstraint = 1; AllocationAffinityConstraints allocationAffinityAttribute = 2; } // Affinity to node, multiple AffinityTargetExpression will be specified, // They will be connected by AND. message NodeAffinityConstraints { repeated AffinityTargetExpression targetExpressions = 2; } // Affinity to allocations (containers). // Affinity is single-direction, which means if RM wants to do mutual affinity/ // anti-affinity between allocations, same constraints need to be added // to all allocation asks. message AllocationAffinityConstraints { // Scope: scope is key of node attribute, which determines if >1 allocations // in the same group or not. // When allocations on node(s) which have same node attribute value // for given node attribute key == scope. They're in the same group. // // e.g. when user wants to do anti-affinity between allocation on node // basis, scope can be set to "hostname", max-cardinality = 1; string scope = 1; repeated AffinityTargetExpression tragetExpressions = 2; int32 minCardinality = 3; int32 maxCardinality = 4; // Is this a required (hard) or preferred (soft) request. bool required = 5; } message AffinityTargetExpression { // Following 4 operators can be specified, by default is "IN". // When EXIST/NOT_EXISTS specified, scheduler only check if given targetKey // appears on node attribute or allocation tag. enum AffinityTargetOperator { IN = 0; NOT_IN = 1; EXIST = 2; NOT_EXIST = 3; } AffinityTargetExpression targetOperator = 1; string targetKey = 2; repeated string targetValues = 3; }
As mentioned above, the intention is to support Composite Placement Constraint in the future.
The following protocol block is not marked as protobuf code and is added as a reference only and will not be processed as part of the protocol generation.
message CompositePlacementConstraintProto {
enum CompositeType {
// All children constraints have to be satisfied.
AND = 0;
// One of the children constraints has to be satisfied.
OR = 1;
// Attempt to satisfy the first child constraint for delays[0] units (e.g.,
// millisec or heartbeats). If this fails, try to satisfy the second child
// constraint for delays[1] units and so on.
DELAYED_OR = 2;
}
CompositeType compositeType = 1;
repeated PlacementConstraintProto childConstraints = 2;
repeated TimedPlacementConstraintProto timedChildConstraints = 3;
}
message TimedPlacementConstraintProto {
enum DelayUnit {
MILLISECONDS = 0;
OPPORTUNITIES = 1;
}
required PlacementConstraintProto placementConstraint = 1;
required int64 schedulingDelay = 2;
DelayUnit delayUnit = 3 [ default = MILLISECONDS ];
}
message AllocationReleasesRequest { repeated AllocationReleaseRequest allocationsToRelease = 1; repeated AllocationAskReleaseRequest allocationAsksToRelease = 2; } // Release allocation message AllocationReleaseRequest { // optional, when this is set, only release allocation by given uuid. string uuid = 1; // when this is set, filter allocations by application id. // empty value will filter allocations don't belong to application. // when application id is set and uuid not set, release all allocations under the application id. string applicationId = 2; // Which partition to release, required. string partitionName = 3; // For human-readable string message = 4; } // Release allocation message AllocationAskReleaseRequest { // optional, when this is set, only release allocation ask by specified string allocationkey = 1; // when this is set, filter allocation key by application id. // empty value will filter allocations don't belong to application. // when application id is set and allocationKey not set, release all allocations key under the application id. string applicationId = 2; // Which partition to release, required. string partitionName = 3; // For human-readable string message = 4; }
State transition of node:
+-----------+ +--------+ +-------+
|SCHEDULABLE|+-------->|DRAINING|+---------->|REMOVED|
+-----------+ +--------+ +-------+
^ Asked by + Aasked by
| RM to DRAIN | RM to REMOVE
| |
+---------------------+
Asked by RM to
SCHEDULE again
See protocol below:
Registration of a new node with the scheduler
message NewNodeInfo { // Id of node, it should be identical if same node daemon restarted. string nodeId = 1; // node attributes map<string, string> attributes = 2; // Schedulable Resource, scheduler may overcommit resource of node depends on available information // (such as utilization, priority of each container, etc.) Resource schedulableResource = 3; // Allocated resources, this will be added when node registered to RM // (recovery) repeated Allocation existingAllocations = 4; }
Update of a registered node with the scheduler
message UpdateNodeInfo { // Action from RM enum ActionFromRM { // Do not allocate new allocations on the node. DRAIN_NODE = 0; // Decomission node, it will immediately stop allocations on the same // node and move the node from schedulable lists. DECOMISSION = 1; // From Draining state to SCHEDULABLE state. // If node is not in draining state, error will be thrown DRAIN_TO_SCHEDULABLE = 2; } // Id of node string nodeId = 1; // New attributes of node, which will replace previously reported attribute. map<string, string> attributes = 2; // new schedulable resource, scheduler may preempt allocations on the // node or schedule more allocations accordingly. Resource schedulableResource = 3; ActionFromRM action = 4; }
message UtilizationReport { // it could be either node id or allocation uuid. string id = 1; // Actual used resource Resource actualUsedResource = 2; }
Following is feedback from scheduler to RM:
Allocation is allocated allocations from scheduler.
message Allocation { // AllocationKey from AllocationAsk string allocationKey = 1; // Allocation tags from AllocationAsk map<string, string> allocationTags = 2; // uuid of the allocation string uuid = 3; // Resource for each allocation Resource resourcePerAlloc = 5; // Priority of ask Priority priority = 6; // Queue which the allocation belongs to string queueName = 7; // Node which the allocation belongs to string nodeId = 8; // Id of Application string applicationId = 9; // Partition of the allocation string partition = 10; }
When allocation ask rejected by scheduler, information will be shared by scheduler.
message RejectedAllocationAsk { string allocationKey = 1; string applicationId = 2; string reason = 3; }
Scheduler can notify suggestions to RM about node. This can be either human-readable or actions can be taken.
message NodeRecommendation { Resource recommendedSchedulableResource = 1; // Any other human-readable message string message = 2; }
For released allocations
// When allocation released, either by RM or preempted by scheduler. It will be sent back to RM. message AllocationReleaseResponse { enum TerminationType { // STOPPED by ResourceManager. STOPPED_BY_RM = 0; // TIMEOUT (when timeout of allocation set) TIMEOUT = 1; // PREEMPTED BY SCHEDULER PREEMPTED_BY_SCHEDULER = 2; } // UUID of allocation. string allocationUUID = 1; // Why terminated TerminationType terminationType = 2; // Message (for human readble) string message = 3; }
Scheduler Interface reserved all attribute in si.io namespace.
Known attribute names for nodes and applications.
// Constants for node attribtues const ( ARCH="si.io/arch" HOSTNAME="si.io/hostname" RACKNAME="si.io/rackname" OS="si.io/os" INSTANCE_TYPE="si.io/instance-type" FAILURE_DOMAIN_ZONE="si.io/zone" FAILURE_DOMAIN_REGION="si.io/region" LOCAL_IMAGES="si.io/local-images" NODE_PARTITION="si.io/node-partition" ) // Constants for allocation attribtues const ( APPLICATION_ID="si.io/application-id" CONTAINER_IMAGE="si.io/container-image" CONTAINER_PORTS="si.io/container-ports" )