Introduction
- The Agent Cluster brings horizontal scalability and fail-over capabilities to Agents.
- A number of Subagents operated for different servers share the job execution load in an Agent Cluster (active clustering).
- Automated fail-over guarantees high-availability and restart capabilities of an Agent Cluster (passive cluster).
- The Agent Cluster is subject to the agreements of the JS7 - License.
- Development
Operational View
The architecture applies to the clustering of Agent Directors and the clustering of Subagents for high-availability and scalability.
- The components involved in an Agent Cluster are represented as one Agent to the Controller.
- A Controller can manage any number of Agents either from different Agent Clusters or as a number of Standalone Agents.
Agent Director
The Agent Director ships with an Integrated Subagent that runs inside the Director.
- The Subagent is instructed by the active Director to execute jobs. The Director instance holding the active role can be the Subagent's Director or a second Director.
- The Director's Subagent can be optionally disabled in order to have the Director perform only orchestration and not execute jobs with its Subagent.
The Agent Director is contacted by the Controller for deployment of scheduling objects, for commands that change an order's state such as suspend, resume and cancel, and to report back the results of executing JS7 - Workflow Instructions.
Director Journal
The Agent Director holds a journal to store
- scheduling objects such as workflows and jobs that are deployed via a Controller,
- events about JS7 - Order State Transitions and log output reported from Subagents executing jobs.
The journal is essential for the restarting capabilities of the Agent Director.
Director Cluster
The Agent Director can be operated as a Standalone instance and as a member in a Director Cluster of two Agent Directors.
In a Director Cluster one Director holds the active role and the second Director holds the passive role.
If the Agent Director is operated as a cluster then the active Director synchronizes its journal with the standby Director. If the journals of both active and standby Directors are in sync then a fail-over (automatically) or switch-over (caused by user intervention) can occur and Directors switch active and standby roles.
Subagent
Subagents come in two shapes: they ship with an Agent Director and they can be operated as Standalone instances.
- Subagents are lightweight and do not operate a journal.
- Subagents are deployed to any number of servers in a network.
- Subagents are closely monitored by Agent Directors using bi-directional heartbeats.
Job Execution
Subagents execute jobs and report back execution results.
- Subagents execute jobs on behalf of the active Agent Director.
- They report back log output and the execution results of jobs to the active Agent Director.
- If a Subagent fails then the active Agent Director will hand-over the job execution request to the next Subagent.
- A Subagent kills running jobs if the connection from the active Agent Director is lost or if it is instructed by the active Agent Director to suspend/kill or to cancel/kill an order.
- This behavior is intended to prevent double job execution by more than one Subagent.
- If the connection from the active Agent Director can be re-established within a given timeout then the Subagent will continue to execute jobs.
Subagent Cluster
Subagents can be grouped into clusters.
- A Subagent Cluster is specified by a Selection and Scheduling Mode:
- The cluster can include a single Subagent, a number of Subagents or all Subagents.
- The Scheduling Mode is one of fixed-priority or round-robin.
- Any number of Subagent Clusters can be configured.
Functional View
Jobs in workflows are assigned a Subagent Cluster that includes a Selection and Scheduling Mode of Subagents:
Subagent Cluster
Jobs in workflows are assigned a Subagent Cluster that includes a Selection and Scheduling Mode of Subagents:
- Subagent Clusters present a logical view of the way a given number of Subagents co-operate for job execution.
- Any number of Subagent Clusters can be configured using the same Subagents.
- The Selection makes use of one or more Subagents.
- Subagents are used for job execution according to their ordering in the Selection.
- A Subagent can be a member in one or more Subagent Clusters.
- The configuration of Subagent Clusters is performed using the JOC Cockpit and is forwarded to the Controller and to the active Agent Director.
- The Scheduling Mode is one of:
- fixed-priority: execute jobs with the first Subagent and switch to the next Subagent only if the first Subagent becomes unavailable (passive clustering).
- round-robin: execute each next job on the next Subagent (active clustering).
Network Connections
Network connections use the HTTP protocol and can be secured using TLS/SSL certificates.
Connections are unidirectional and are established:
- by the Controller to the Agent Director,
- by the Agent Director to the Subagent.
Workflow Execution
Workflows are deployed from the JOC Cockpit to a Controller and are forwarded to the Agent Director. Similarly, orders are submitted to a Controller and to the relevant Agent Director.
Orders are scheduled for a given date and time at which the Agent Director will start the workflow.
- The Agent Director will execute a number of JS7 - Workflow Instructions, for example Retry, Try/Catch, Fork, which are in the scope of the Agent Director.
- The Agent Director will request execution of jobs as available from the JS7 - Job Instruction with a Subagent. When choosing the Subagent the Agent Director considers the Selection of Subagents and Scheduling Mode of the Subagent Cluster that is assigned the job. For example, a specific Subagent will be selected for a fixed-priority Scheduling Mode.
- The Agent Director will hand back the order to the Controller if it meets an instruction that is out of the scope of a single Agent, for example in case of a JS7 - Lock Instruction.
Overview
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