[jira] [Commented] (SLING-4603) oak-documentMk based discovery.impl
[
https://issues.apache.org/jira/browse/SLING-4603?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanelfocusedCommentId=14530529#comment-14530529
]
Stefan Egli commented on SLING-4603:
Note that meanwhile an alternative approach is suggested in OAK-2844 - pending
comments/reviews. That would change the way SLING-4603 would go forward: the
idea would be to use suggested discovery-light API of OAK-2844 instead of going
via JMX.
oak-documentMk based discovery.impl
---
Key: SLING-4603
URL: https://issues.apache.org/jira/browse/SLING-4603
Project: Sling
Issue Type: New Feature
Components: Extensions
Reporter: Stefan Egli
Assignee: Stefan Egli
When discovery is used in a stack based on jackrabbit oak as the repository,
the current way of discoving instances somewhat sounds like duplicating work:
oak, or more precisely documentnodestore, itself has a low-level [lease
mechanism|http://jackrabbit.apache.org/oak/docs/nodestore/documentmk.html]
where it stores information about the cluster nodes including a {{leaseEnd}}
indicating at what time others can consider a particular node as
dead/crashed. This corresponds pretty much to the discovery.impl heartbeat
mechanism. And in a stack which is built ontop of oak-documentMk, we could be
making use of this fact and delegate the decision about whether a node in a
cluster is alive or not to the oak layer. Also, with OAK-2597 the relevant
information: {{ActiveClusterNodes}} is nicely exposed via JMX - so that can
become the new source of truth defining the cluster view.
When replacing discovery-owned heartbeats with oak-owned ones, there is one
important detail to be watched out for: it can no longer easily be determined
from another instance in the cluster, whether it has this new discovery
bundle activated or not. Hence it is not given that when a voting happens,
that all {{active}} nodes (as reported by oak-documentMk) are actually going
to respond. So the 'silent instance due to deactivated discovery bundle' case
needs special attention/handling.
Other than that, given the normal case of all {{active}} nodes having the
bundle activated, the voting mechanism can stay the same as in
discovery.impl. The topology connectors can be treated the same too (by
storing announcements to their respective
{{/var/discovery/clusterInstances/slingId/announcements/announcerSlingId}}
node. The properties can be handled the same too (by storing to
{{/properties}} node. Only thing that gets replaced is the {{heartbeats}}.
Note that in order for such an oak-based discovery.impl this oak-lease
mechanism must be very robust (it should be so by its own interest already).
However, there are currently a few issues that should probably first be
resolved until discovery can be based on this: OAK-2739, OAK-2682 and
OAK-2681 are currently known in this area.
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[jira] [Commented] (SLING-4603) oak-documentMk based discovery.impl
[
https://issues.apache.org/jira/browse/SLING-4603?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanelfocusedCommentId=14495858#comment-14495858
]
Stefan Egli commented on SLING-4603:
Also started a discussion on oak-dev list wrt JMX vs API for this:
http://markmail.org/thread/2tdnulytfs4su6mo
oak-documentMk based discovery.impl
---
Key: SLING-4603
URL: https://issues.apache.org/jira/browse/SLING-4603
Project: Sling
Issue Type: New Feature
Components: Extensions
Reporter: Stefan Egli
Assignee: Stefan Egli
When discovery is used in a stack based on jackrabbit oak as the repository,
the current way of discoving instances somewhat sounds like duplicating work:
oak, or more precisely documentnodestore, itself has a low-level [lease
mechanism|http://jackrabbit.apache.org/oak/docs/nodestore/documentmk.html]
where it stores information about the cluster nodes including a {{leaseEnd}}
indicating at what time others can consider a particular node as
dead/crashed. This corresponds pretty much to the discovery.impl heartbeat
mechanism. And in a stack which is built ontop of oak-documentMk, we could be
making use of this fact and delegate the decision about whether a node in a
cluster is alive or not to the oak layer. Also, with OAK-2597 the relevant
information: {{ActiveClusterNodes}} is nicely exposed via JMX - so that can
become the new source of truth defining the cluster view.
When replacing discovery-owned heartbeats with oak-owned ones, there is one
important detail to be watched out for: it can no longer easily be determined
from another instance in the cluster, whether it has this new discovery
bundle activated or not. Hence it is not given that when a voting happens,
that all {{active}} nodes (as reported by oak-documentMk) are actually going
to respond. So the 'silent instance due to deactivated discovery bundle' case
needs special attention/handling.
Other than that, given the normal case of all {{active}} nodes having the
bundle activated, the voting mechanism can stay the same as in
discovery.impl. The topology connectors can be treated the same too (by
storing announcements to their respective
{{/var/discovery/clusterInstances/slingId/announcements/announcerSlingId}}
node. The properties can be handled the same too (by storing to
{{/properties}} node. Only thing that gets replaced is the {{heartbeats}}.
Note that in order for such an oak-based discovery.impl this oak-lease
mechanism must be very robust (it should be so by its own interest already).
However, there are currently a few issues that should probably first be
resolved until discovery can be based on this: OAK-2739, OAK-2682 and
OAK-2681 are currently known in this area.
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[jira] [Commented] (SLING-4603) oak-documentMk based discovery.impl
[
https://issues.apache.org/jira/browse/SLING-4603?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanelfocusedCommentId=14491937#comment-14491937
]
Felix Meschberger commented on SLING-4603:
--
See discussion in http://sling.markmail.org/thread/rrodyxlxoiuyx74d
oak-documentMk based discovery.impl
---
Key: SLING-4603
URL: https://issues.apache.org/jira/browse/SLING-4603
Project: Sling
Issue Type: New Feature
Components: Extensions
Reporter: Stefan Egli
Assignee: Stefan Egli
When discovery is used in a stack based on jackrabbit oak as the repository,
the current way of discoving instances somewhat sounds like duplicating work:
oak, or more precisely documentnodestore, itself has a low-level [lease
mechanism|http://jackrabbit.apache.org/oak/docs/nodestore/documentmk.html]
where it stores information about the cluster nodes including a {{leaseEnd}}
indicating at what time others can consider a particular node as
dead/crashed. This corresponds pretty much to the discovery.impl heartbeat
mechanism. And in a stack which is built ontop of oak-documentMk, we could be
making use of this fact and delegate the decision about whether a node in a
cluster is alive or not to the oak layer. Also, with OAK-2597 the relevant
information: {{ActiveClusterNodes}} is nicely exposed via JMX - so that can
become the new source of truth defining the cluster view.
When replacing discovery-owned heartbeats with oak-owned ones, there is one
important detail to be watched out for: it can no longer easily be determined
from another instance in the cluster, whether it has this new discovery
bundle activated or not. Hence it is not given that when a voting happens,
that all {{active}} nodes (as reported by oak-documentMk) are actually going
to respond. So the 'silent instance due to deactivated discovery bundle' case
needs special attention/handling.
Other than that, given the normal case of all {{active}} nodes having the
bundle activated, the voting mechanism can stay the same as in
discovery.impl. The topology connectors can be treated the same too (by
storing announcements to their respective
{{/var/discovery/clusterInstances/slingId/announcements/announcerSlingId}}
node. The properties can be handled the same too (by storing to
{{/properties}} node. Only thing that gets replaced is the {{heartbeats}}.
Note that in order for such an oak-based discovery.impl this oak-lease
mechanism must be very robust (it should be so by its own interest already).
However, there are currently a few issues that should probably first be
resolved until discovery can be based on this: OAK-2739, OAK-2682 and
OAK-2681 are currently known in this area.
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