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V4/Monitor Replication Topology

Name: V4/Monitor Replication Topology
Ticket: #4390
Author: LKrispen
Incomplete.png Pending review
Last updated: 2016-06-10 by Mkosek

Overview

In a replication topology there exist many replication agreements and to monitor the state of these agreements each of the servers in the topology has to be queried. With the deployment of the topology plugin it is possible to have the complete view of the topology on any server. This paper describes how the topology plugin functions can be etxended to provide replication monitoring.

Use Cases

TODO

Design

The feature is implemented as an extension to the topology plugin. It implements a query for replication state, which is propagated to all servers in the topology, the result of the query is conatained in the topology segments and can be listed or visualized by contacting any server.

New attributes in topology objects

The suffix and segment entries will be extended to manage monitoring requests and responses

Extension of the ipaReplicationTopologyConfig entry:

cn=<replica>,cn=topology,<shared topology config base>
objectclass: ipaReplicationTopologyConfig
ipaReplTopoConfigRoot: < dn >
ipaReplTopoMonitorRequest: <request ID>

The request ID is used to map the monitoring responses to a request, to trigger a new request a ldap replace operation for this attribute is applied. A simple time stamp is used as requestID.

Extension to the ipaReplicationTopologySegment:

cn: <uniquename defining the segment>, cn=<replica>,cn=topology,<shared topology config base>
objectclass: ipaReplicationTopologySegment
ipaReplSegmenState;left : <requestID>:<replication state>
ipaReplSegmenState;right : <requestID>:<replication state>

For each agreement a replication state attribute is added ";left" ";right" indicate to which of the two agreements that can be represented by a segment the information refers

plugin operation

The topology plugin monitors updates to the ipaReplTopoMonitorRequest attribute, if this attribute is replaced wit a new monitoringID it checks the status of the local agreements and updates the ipaReplTopoState attributes in the corresponding segments. These updates will be replicated to the other replicas

Monitoring procedure

A client, CLI or GUI, initiates a monitoring cycle by modifying the ipaReplTopoMonitorRequest attribute on one server. It then contacts this, or any otehr, server and reads the topology segments for the monitored suffix. It may take some time until the state information has been updated on all servers and finally replicated, so this maybe has to be repeated until a defined maximal waiting period passed.

Based on the received information, the state of the agreements can be listed. The state of the agreement will be:

green: the agrement is operational
red: agreement is not working (no more refinements yet)
grey: no response for the monitoring request with the given monitoringID was received

Required actions

If all agreements are "green", no actions required

For "red" agreements further investigation on the affected serves is required.

If "grey" agreements exist, this means that part of the topology cannot be reached by the server where the monitoring request was issued. Send the monitoring request with the same monitoringID to a server in the "grey" area, and merge the monitoring information for a more complete picture of replication state.

Implementation

Any implementation details you would like to spell out. Describe any technical details here. Make sure you cover

  • Dependencies: any new dependencies that FreeIPA project or it's part would gain and that needs to be packaged in distros?
  • Backup and Restore: any new file to back up or change required in Backup and Restore?

If this section is not trivial, move it to /Implementation sub page and only include link.

Feature Management

UI

TODO

CLI

TODO

Configuration

TODO

Upgrade

TODO

How to Test

TODO

Test Plan

TODO