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Zeebe API (gRPC)

Zeebe clients use gRPC to communicate with the cluster.

Gateway service

The Zeebe client gRPC API is exposed through a single gateway service. The current version of the protocol buffer file can be found in the Zeebe repository.

ActivateJobs RPC

Iterates through all known partitions round-robin, activates up to the requested maximum, and streams them back to the client as they are activated.

Input: ActivateJobsRequest

message ActivateJobsRequest {
// the job type, as defined in the BPMN process (e.g. <zeebe:taskDefinition
// type="payment-service" />)
string type = 1;
// the name of the worker activating the jobs, mostly used for logging purposes
string worker = 2;
// a job returned after this call will not be activated by another call until the
// timeout (in ms) has been reached
int64 timeout = 3;
// the maximum jobs to activate by this request
int32 maxJobsToActivate = 4;
// a list of variables to fetch as the job variables; if empty, all visible variables at
// the time of activation for the scope of the job will be returned
repeated string fetchVariable = 5;
// The request will be completed when at least one job is activated or after the requestTimeout (in ms).
// if the requestTimeout = 0, a default timeout is used.
// if the requestTimeout < 0, long polling is disabled and the request is completed immediately, even when no job is activated.
int64 requestTimeout = 6;
}

Output: ActivateJobsResponse

message ActivateJobsResponse {
// list of activated jobs
repeated ActivatedJob jobs = 1;
}

message ActivatedJob {
// the key, a unique identifier for the job
int64 key = 1;
// the type of the job (should match what was requested)
string type = 2;
// the job's process instance key
int64 processInstanceKey = 3;
// the bpmn process ID of the job process definition
string bpmnProcessId = 4;
// the version of the job process definition
int32 processDefinitionVersion = 5;
// the key of the job process definition
int64 processKey = 6;
// the associated task element ID
string elementId = 7;
// the unique key identifying the associated task, unique within the scope of the
// process instance
int64 elementInstanceKey = 8;
// a set of custom headers defined during modelling; returned as a serialized
// JSON document
string customHeaders = 9;
// the name of the worker which activated this job
string worker = 10;
// the amount of retries left to this job (should always be positive)
int32 retries = 11;
// when the job can be activated again, sent as a UNIX epoch timestamp
int64 deadline = 12;
// JSON document, computed at activation time, consisting of all visible variables to
// the task scope
string variables = 13;
}

Errors

GRPC_STATUS_INVALID_ARGUMENT

Returned if:

  • Type is blank (empty string, null)
  • Worker is blank (empty string, null)
  • Timeout less than 1 (ms)
  • maxJobsToActivate is less than 1

CancelProcessInstance RPC

Cancels a running process instance.

Input: CancelProcessInstanceRequest

message CancelProcessInstanceRequest {
// the process instance key (as, for example, obtained from
// CreateProcessInstanceResponse)
int64 processInstanceKey = 1;
}

Output: CancelProcessInstanceResponse

message CancelProcessInstanceResponse {
}

Errors

GRPC_STATUS_NOT_FOUND

Returned if:

  • No process instance exists with the given key. Note that since process instances are removed once they are finished, it could mean the instance did exist at some point.

CompleteJob RPC

Completes a job with the given payload, which allows completing the associated service task.

Input: CompleteJobRequest

message CompleteJobRequest {
// the unique job identifier, as obtained from ActivateJobsResponse
int64 jobKey = 1;
// a JSON document representing the variables in the current task scope
string variables = 2;
}

Output: CompleteJobResponse

message CompleteJobResponse {
}

Errors

GRPC_STATUS_NOT_FOUND

Returned if:

  • No job exists with the given job key. Note that since jobs are removed once completed, it could be that this job did exist at some point.
GRPC_STATUS_FAILED_PRECONDITION

Returned if:

  • The job was marked as failed. In that case, the related incident must be resolved before the job can be activated again and completed.

CreateProcessInstance RPC

Creates and starts an instance of the specified process. The process definition to use to create the instance can be specified either using its unique key (as returned by DeployProcess), or using the BPMN process ID and a version. Pass -1 as the version to use the latest deployed version.

note

Only processes with none start events can be started through this command.

Input: CreateProcessInstanceRequest

message CreateProcessInstanceRequest {
// the unique key identifying the process definition (e.g. returned from a process
// in the DeployProcessResponse message)
int64 processDefinitionKey = 1;
// the BPMN process ID of the process definition
string bpmnProcessId = 2;
// the version of the process; set to -1 to use the latest version
int32 version = 3;
// JSON document that will instantiate the variables for the root variable scope of the
// process instance; it must be a JSON object, as variables will be mapped in a
// key-value fashion. e.g. { "a": 1, "b": 2 } will create two variables, named "a" and
// "b" respectively, with their associated values. [{ "a": 1, "b": 2 }] would not be a
// valid argument, as the root of the JSON document is an array and not an object.
string variables = 4;
// List of start instructions. If empty (default) the process instance
// will start at the start event. If non-empty the process instance will apply start
// instructions after it has been created
repeated ProcessInstanceCreationStartInstruction startInstructions = 5;
}

message ProcessInstanceCreationStartInstruction {

// future extensions might include
// - different types of start instructions
// - ability to set local variables for different flow scopes

// for now, however, the start instruction is implicitly a
// "startBeforeElement" instruction

// element ID
string elementId = 1;
}

Output: CreateProcessInstanceResponse

message CreateProcessInstanceResponse {
// the key of the process definition which was used to create the process instance
int64 processKey = 1;
// the BPMN process ID of the process definition which was used to create the process
// instance
string bpmnProcessId = 2;
// the version of the process definition which was used to create the process instance
int32 version = 3;
// the unique identifier of the created process instance; to be used wherever a request
// needs a process instance key (e.g. CancelProcessInstanceRequest)
int64 processInstanceKey = 4;
}

CreateProcessInstanceWithResult RPC

Similar to CreateProcessInstance RPC, creates and starts an instance of the specified process. Unlike CreateProcessInstance RPC, the response is returned when the process is completed.

note

Only processes with none start events can be started through this command.

Input: CreateProcessInstanceWithResultRequest

message CreateProcessInstanceRequest {
CreateProcessInstanceRequest request = 1;
// timeout (in ms). the request will be closed if the process is not completed before
// the requestTimeout.
// if requestTimeout = 0, uses the generic requestTimeout configured in the gateway.
int64 requestTimeout = 2;
}

Output: CreateProcessInstanceWithResultResponse

message CreateProcessInstanceResponse {
// the key of the process definition which was used to create the process instance
int64 processKey = 1;
// the BPMN process ID of the process definition which was used to create the process
// instance
string bpmnProcessId = 2;
// the version of the process definition which was used to create the process instance
int32 version = 3;
// the unique identifier of the created process instance; to be used wherever a request
// needs a process instance key (e.g. CancelProcessInstanceRequest)
int64 processInstanceKey = 4;
// consisting of all visible variables to the root scope
string variables = 5;
}

Errors

GRPC_STATUS_NOT_FOUND

Returned if:

  • No process with the given key exists (if processKey was given).
  • No process with the given process ID exists (if bpmnProcessId was given but version was -1).
  • No process with the given process ID and version exists (if both bpmnProcessId and version were given).
GRPC_STATUS_FAILED_PRECONDITION

Returned if:

  • The process definition does not contain a none start event; only processes with none start event can be started manually.
GRPC_STATUS_INVALID_ARGUMENT

Returned if:

  • The given variables argument is not a valid JSON document; it is expected to be a valid JSON document where the root node is an object.

DeployResource RPC

Deploys one or more resources (e.g. processes or decision models) to Zeebe. Note that this is an atomic call, i.e. either all resources are deployed, or none of them are.

Input: DeployResourceRequest

message DeployResourceRequest {
// list of resources to deploy
repeated Resource resources = 1;
}

message Resource {
// the resource name, e.g. myProcess.bpmn or myDecision.dmn
string name = 1;
// the file content as a UTF8-encoded string
bytes content = 2;
}

Output: DeployResourceResponse

message DeployResourceResponse {
// the unique key identifying the deployment
int64 key = 1;
// a list of deployed resources, e.g. processes
repeated Deployment deployments = 2;
}

message Deployment {
// each deployment has only one metadata
oneof Metadata {
// metadata of a deployed process
ProcessMetadata process = 1;
// metadata of a deployed decision
DecisionMetadata decision = 2;
// metadata of a deployed decision requirements
DecisionRequirementsMetadata decisionRequirements = 3;
}
}

message ProcessMetadata {
// the bpmn process ID, as parsed during deployment; together with the version forms a
// unique identifier for a specific process definition
string bpmnProcessId = 1;
// the assigned process version
int32 version = 2;
// the assigned key, which acts as a unique identifier for this process
int64 processDefinitionKey = 3;
// the resource name (see: ProcessRequestObject.name) from which this process was
// parsed
string resourceName = 4;
}

message DecisionMetadata {
// the dmn decision ID, as parsed during deployment; together with the
// versions forms a unique identifier for a specific decision
string dmnDecisionId = 1;
// the dmn name of the decision, as parsed during deployment
string dmnDecisionName = 2;
// the assigned decision version
int32 version = 3;
// the assigned decision key, which acts as a unique identifier for this
// decision
int64 decisionKey = 4;
// the dmn ID of the decision requirements graph that this decision is part
// of, as parsed during deployment
string dmnDecisionRequirementsId = 5;
// the assigned key of the decision requirements graph that this decision is
// part of
int64 decisionRequirementsKey = 6;
}

message DecisionRequirementsMetadata {
// the dmn decision requirements ID, as parsed during deployment; together
// with the versions forms a unique identifier for a specific decision
string dmnDecisionRequirementsId = 1;
// the dmn name of the decision requirements, as parsed during deployment
string dmnDecisionRequirementsName = 2;
// the assigned decision requirements version
int32 version = 3;
// the assigned decision requirements key, which acts as a unique identifier
// for this decision requirements
int64 decisionRequirementsKey = 4;
// the resource name (see: Resource.name) from which this decision
// requirements was parsed
string resourceName = 5;
}

Errors

GRPC_STATUS_INVALID_ARGUMENT

Returned if:

  • No resources given.
  • At least one resource is invalid. A resource is considered invalid if:
    • The resource type is not supported (e.g. supported resources include BPMN and DMN files)
    • The content is not deserializable (e.g. detected as BPMN, but it's broken XML)
    • The content is invalid (e.g. an event-based gateway has an outgoing sequence flow to a task)

FailJob RPC

Marks the job as failed. If the retries argument is positive and no retry back off is set, the job is immediately activatable again. If the retry back off is positive the job becomes activatable once the back off timeout has passed. If the retries argument is zero or negative, an incident is raised, tagged with the given errorMessage, and the job is not activatable until the incident is resolved.

Input: FailJobRequest

message FailJobRequest {
// the unique job identifier, as obtained when activating the job
int64 jobKey = 1;
// the amount of retries the job should have left
int32 retries = 2;
// an optional message describing why the job failed
// this is particularly useful if a job runs out of retries and an incident is raised,
// as it this message can help explain why an incident was raised
string errorMessage = 3;
// the backoff timeout (in ms) for the next retry
int64 retryBackOff = 4;
}

Output: FailJobResponse

message FailJobResponse {
}

Errors

GRPC_STATUS_NOT_FOUND

Returned if:

  • No job was found with the given key.
GRPC_STATUS_FAILED_PRECONDITION

Returned if:

  • The job was not activated.
  • The job is already in a failed state, i.e. ran out of retries.

ModifyProcessInstance RPC

Modifies a running process instance. The command can contain multiple instructions to activate an element of the process, or to terminate an active instance of an element.

Use the command to repair a process instance that is stuck on an element or took an unintended path. For example, because an external system is not available or doesn't respond as expected.

Input: ModifyProcessInstanceRequest

message ModifyProcessInstanceRequest {
// the key of the process instance that should be modified
int64 processInstanceKey = 1;
// instructions describing which elements should be activated in which scopes,
// and which variables should be created
repeated ActivateInstruction activateInstructions = 2;
// instructions describing which elements should be terminated
repeated TerminateInstruction terminateInstructions = 3;

message ActivateInstruction {
// the id of the element that should be activated
string elementId = 1;
// the key of the ancestor scope the element instance should be created in;
// set to -1 to create the new element instance within an existing element
// instance of the flow scope
int64 ancestorElementInstanceKey = 2;
// instructions describing which variables should be created
repeated VariableInstruction variableInstructions = 3;
}

message VariableInstruction {
// JSON document that will instantiate the variables for the root variable scope of the
// process instance; it must be a JSON object, as variables will be mapped in a
// key-value fashion. e.g. { "a": 1, "b": 2 } will create two variables, named "a" and
// "b" respectively, with their associated values. [{ "a": 1, "b": 2 }] would not be a
// valid argument, as the root of the JSON document is an array and not an object.
string variables = 1;
// the id of the element in which scope the variables should be created;
// leave empty to create the variables in the global scope of the process instance
string scopeId = 2;
}

message TerminateInstruction {
// the id of the element that should be terminated
int64 elementInstanceKey = 1;
}
}

Output: ModifyProcessInstanceResponse

message ModifyProcessInstanceResponse {
}

Errors

GRPC_STATUS_NOT_FOUND

Returned if:

  • No process instance exists with the given key, or it is not active.
GRPC_STATUS_INVALID_ARGUMENT

Returned if:

  • At least one activate instruction is invalid. An activate instruction is considered invalid if:
    • The process doesn't contain an element with the given id.
    • A flow scope of the given element can't be created.
    • The given element has more than one active instance of its flow scope.
  • At least one variable instruction is invalid. A variable instruction is considered invalid if:
    • The process doesn't contain an element with the given scope id.
    • The given element doesn't belong to the activating element's flow scope.
    • The given variables are not a valid JSON document.
  • At least one terminate instruction is invalid. A terminate instruction is considered invalid if:
    • No element instance exists with the given key, or it is not active.
  • The instructions would terminate all element instances of a process instance that was created by a call activity in the parent process.

PublishMessage RPC

Publishes a single message. Messages are published to specific partitions computed from their correlation keys.

Input: PublishMessageRequest

message PublishMessageRequest {
// the name of the message
string name = 1;
// the correlation key of the message
string correlationKey = 2;
// how long the message should be buffered on the broker, in milliseconds
int64 timeToLive = 3;
// the unique ID of the message; can be omitted. only useful to ensure only one message
// with the given ID will ever be published (during its lifetime)
string messageId = 4;
// the message variables as a JSON document; to be valid, the root of the document must be an
// object, e.g. { "a": "foo" }. [ "foo" ] would not be valid.
string variables = 5;
}

Output: PublishMessageResponse

message PublishMessageResponse {
// the unique ID of the message that was published
int64 key = 1;
}

Errors

GRPC_STATUS_ALREADY_EXISTS

Returned if:

  • A message with the same ID was previously published (and is still alive).

ResolveIncident RPC

Resolves a given incident. This simply marks the incident as resolved; most likely a call to UpdateJobRetries or SetVariables will be necessary to actually resolve the problem, followed by this call.

Input: ResolveIncidentRequest

message ResolveIncidentRequest {
// the unique ID of the incident to resolve
int64 incidentKey = 1;
}

Output: ResolveIncidentResponse

message ResolveIncidentResponse {
}

Errors

GRPC_STATUS_NOT_FOUND

Returned if:

  • No incident with the given key exists.

SetVariables RPC

Updates all the variables of a particular scope (e.g. process instance, flow element instance) from the given JSON document.

Input: SetVariablesRequest

message SetVariablesRequest {
// the unique identifier of a particular element; can be the process instance key (as
// obtained during instance creation), or a given element, such as a service task (see
// elementInstanceKey on the job message)
int64 elementInstanceKey = 1;
// a JSON serialized document describing variables as key value pairs; the root of the document
// must be an object
string variables = 2;
// if true, the variables will be merged strictly into the local scope (as indicated by
// elementInstanceKey); this means the variables is not propagated to upper scopes.
// for example, let's say we have two scopes, '1' and '2', with each having effective variables as:
// 1 => `{ "foo" : 2 }`, and 2 => `{ "bar" : 1 }`. if we send an update request with
// elementInstanceKey = 2, variables `{ "foo" : 5 }`, and local is true, then scope 1 will
// be unchanged, and scope 2 will now be `{ "bar" : 1, "foo" 5 }`. if local was false, however,
// then scope 1 would be `{ "foo": 5 }`, and scope 2 would be `{ "bar" : 1 }`.
bool local = 3;
}

Output: SetVariablesResponse

message SetVariablesResponse {
// the unique key of the set variables command
int64 key = 1;
}

Errors

GRPC_STATUS_NOT_FOUND

Returned if:

  • No element with the given elementInstanceKey exists.
GRPC_STATUS_INVALID_ARGUMENT

Returned if:

  • The given payload is not a valid JSON document; all payloads are expected to be valid JSON documents where the root node is an object.

ThrowError RPC

Throw an error to indicate that a business error has occurred while processing the job. The error is identified by an error code and is caught by an error catch event with the same error code.

Input: ThrowErrorRequest

message ThrowErrorRequest {
// the unique job identifier, as obtained when activating the job
int64 jobKey = 1;
// the error code that will be matched with an error catch event
string errorCode = 2;
// an optional error message that provides additional context
string errorMessage = 3;
}

Output: ThrowErrorResponse

message ThrowErrorResponse {
}

Errors

GRPC_STATUS_NOT_FOUND

Returned if:

  • No job was found with the given key.
GRPC_STATUS_FAILED_PRECONDITION

Returned if:

  • The job is already in a failed state, i.e. ran out of retries.

Topology RPC

Obtains the current topology of the cluster the gateway is part of.

Input: TopologyRequest

message TopologyRequest {
}

Output: TopologyResponse

message TopologyResponse {
// list of brokers part of this cluster
repeated BrokerInfo brokers = 1;
// how many nodes are in the cluster
int32 clusterSize = 2;
// how many partitions are spread across the cluster
int32 partitionsCount = 3;
// configured replication factor for this cluster
int32 replicationFactor = 4;
// gateway version
string gatewayVersion = 5;
}

message BrokerInfo {
// unique (within a cluster) node ID for the broker
int32 nodeId = 1;
// hostname of the broker
string host = 2;
// port for the broker
int32 port = 3;
// list of partitions managed or replicated on this broker
repeated Partition partitions = 4;
// broker version
string version = 5;
}

message Partition {
// Describes the Raft role of the broker for a given partition
enum PartitionBrokerRole {
LEADER = 0;
FOLLOWER = 1;
}

// Describes the current health of the partition
enum PartitionBrokerHealth {
HEALTHY = 0;
UNHEALTHY = 1;
}

// the unique ID of this partition
int32 partitionId = 1;
// the role of the broker for this partition
PartitionBrokerRole role = 2;
// the health of this partition
PartitionBrokerHealth health = 3;
}

Errors

No specific errors.

UpdateJobRetries RPC

Updates the number of retries a job has left. This is mostly useful for jobs that have run out of retries, should the underlying problem be solved.

Input: UpdateJobRetriesRequest

message UpdateJobRetriesRequest {
// the unique job identifier, as obtained through ActivateJobs
int64 jobKey = 1;
// the new amount of retries for the job; must be positive
int32 retries = 2;
}

Output: UpdateJobRetriesResponse

message UpdateJobRetriesResponse {
}

Errors

GRPC_STATUS_NOT_FOUND

Returned if:

  • No job exists with the given key.
GRPC_STATUS_INVALID_ARGUMENT

Returned if:

  • Retries is not greater than 0.

Technical error handling

In the documentation above, the documented errors are business logic errors. These errors are a result of request processing logic, and not serialization, network, or other more general errors. These errors are described in this section.

The gRPC API for Zeebe is exposed through an API gateway, which acts as a proxy for the cluster. Generally, this means the clients execute a remote call on the gateway, which is then translated to special binary protocol the gateway uses to communicate with nodes in the cluster. The nodes in the cluster are called brokers.

Technical errors which occur between gateway and brokers (e.g. the gateway cannot deserialize the broker response, the broker is unavailable, etc.) are reported to the client using the following error codes:

  • GRPC_STATUS_RESOURCE_EXHAUSTED: When a broker receives more requests than it can handle, it signals backpressure and rejects requests with this error code.
    • In this case, it is possible to retry the requests with an appropriate retry strategy.
    • If you receive many such errors within a short time period, it indicates the broker is constantly under high load.
    • It is recommended to reduce the rate of requests. When backpressure is active, the broker may reject any request except CompleteJob RPC and FailJob RPC.
    • These requests are white-listed for backpressure and are always accepted by the broker even if it is receiving requests above its limits.
  • GRPC_STATUS_UNAVAILABLE: If the gateway itself is in an invalid state (e.g. out of memory).
  • GRPC_STATUS_INTERNAL: For any other internal errors that occurred between the gateway and the broker.

This behavior applies to every request. In these cases, the client should retry with an appropriate retry policy (e.g. a combination of exponential backoff or jitter wrapped in a circuit breaker).

As the gRPC server/client is based on generated code, keep in mind that any call made to the server can also return errors as described by the spec here.

Deprecated RPCs

The following RPCs are exposed by the gateway service, but have been deprecated.

DeployProcess RPC

note

Deprecated since 8, replaced by DeployResource RPC.

Deploys one or more processes to Zeebe. Note that this is an atomic call, i.e. either all processes are deployed, or none of them are.

Input: DeployProcessRequest

message DeployProcessRequest {
// List of process resources to deploy
repeated ProcessRequestObject processes = 1;
}

message ProcessRequestObject {
enum ResourceType {
// FILE type means the gateway will try to detect the resource type
// using the file extension of the name field
FILE = 0;
BPMN = 1; // extension 'bpmn'
YAML = 2 [deprecated = true]; // extension 'yaml'; removed as of release 1.0
}

// the resource basename, e.g. myProcess.bpmn
string name = 1;
// the resource type; if set to BPMN or YAML then the file extension
// is ignored
// As of release 1.0, YAML support was removed and BPMN is the only supported resource type.
// The field was kept to not break clients.
ResourceType type = 2 [deprecated = true];
// the process definition as a UTF8-encoded string
bytes definition = 3;
}

Output: DeployProcessResponse

message DeployProcessResponse {
// the unique key identifying the deployment
int64 key = 1;
// a list of deployed processes
repeated ProcessMetadata processes = 2;
}

message ProcessMetadata {
// the bpmn process ID, as parsed during deployment; together with the version forms a
// unique identifier for a specific process definition
string bpmnProcessId = 1;
// the assigned process version
int32 version = 2;
// the assigned key, which acts as a unique identifier for this process
int64 processKey = 3;
// the resource name (see: ProcessRequestObject.name) from which this process was
// parsed
string resourceName = 4;
}

Errors

GRPC_STATUS_INVALID_ARGUMENT

Returned if:

  • No resources given.
  • At least one resource is invalid. A resource is considered invalid if:
    • It is not a BPMN or YAML file (currently detected through the file extension).
    • The resource data is not deserializable (e.g. detected as BPMN, but it's broken XML).
    • The process is invalid (e.g. an event-based gateway has an outgoing sequence flow to a task.)