HROLLER(1)

HROLLER(1) 💖

okay bestie, welcome to the hroller page — that's the Cluster rolling maintenance scheduler for Ganeti, and yes she's serving Version 3.1.0~rc2 energy, no cap. sit down, hydrate, let's go 🫶

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✨ SYNOPSIS ✨

hroller {backend options...} [algorithm options...]  [reporting options...]

hroller --version

Backend options:

{ -m cluster | -L[ path ] | -t data-file | -I path }

[ --force ]

Algorithm options:

[ -G *name* ] [ -O *name...* ] [ --node-tags tag,.. ] [
--skip-non-redundant ]

[ --offline-maintenance ] [ --ignore-non-redundant ]

Reporting options:

[ -v...  | -q ] [ -S *file* ] [ --one-step-only ] [ --print-moves ]

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🌸 DESCRIPTION 🌸

so hroller is literally a cluster maintenance reboot scheduler. her whole thing? she figures out which set of nodes can be rebooted at the same time while making sure you never end up with both primary and secondary nodes being rebooted at the same time. it's giving careful, it's giving responsible, it's giving main character who actually read the docs 💅

for backends that support identifying the master node — and currently that's RAPI and LUXI — the master node is scheduled as the last node in the last reboot group. and apart from that one little restriction? larger reboot groups are put first. slay.

🧚 ALGORITHM FOR CALCULATING OFFLINE REBOOT GROUPS 🧚

ngl this part is kind of iconic. here's the tea:

hroller views the nodes as vertices of an undirected graph, with two kind of edges:

1. there are edges from the primary to the secondary node of every instance.
2. two nodes are connected by an edge if they are the primary nodes of two instances that have the same secondary node.

then she colors the graph using a few different heuristics, and returns the minimum-size color set found. nodes with the same color can then simultaneously migrate all instance off to their respective secondary nodes, and it is safe to reboot them simultaneously. periodt. 🔥

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👑 OPTIONS 👑

for a description of the standard options check htools(1) and hbal(1). (iykyk)

• --force — do not fail, even if the master node cannot be determined. she's not asking questions, she's just vibing 🫶
• --node-tags tag,... — restrict to nodes having at least one of the given tags.
• --full-evacuation — also plan moving secondaries out of the nodes to be rebooted. for each instance the move is at most a migrate (if it was primary on that node) followed by a replace secondary.
• --skip-non-redundant — restrict to nodes not hosting any non-redundant instance.
• --offline-maintenance — pretend that all instances are shutdown before the reboots are carried out. i.e., only edges from the primary to the secondary node of an instance are considered.
• --ignore-non-redundant — pretend that the non-redundant instances do not exist, and only take instances with primary and secondary node into account.
• --one-step-only — restrict to the first reboot group. output the group one node per line.
• --print-moves — after each group, list for each affected instance a node where it can be evacuated to. the moves are computed under the assumption that after each reboot group, all instances are moved back to their initial position. (those back moves? not in the output, bestie.)

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💀 BUGS 💀

if instances are online, the tool should refuse to do offline rolling maintenances, unless explicitly requested. like… she <should>. 👀

End-to-end shelltests should be provided. yeah. we know. 😭

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🎀 EXAMPLES 🎀

🌈 Online Rolling reboots, using tags 🌈

selecting by tags and getting output for one step only can be used for planing the next maintenance step. :

$ hroller --node-tags needsreboot --one-step-only -L
'First Reboot Group'
 node1.example.com
 node3.example.com

typically these nodes would be drained and migrated. :

$ GROUP=`hroller --node-tags needsreboot --one-step-only --no-headers -L`
$ for node in $GROUP; do gnt-node modify -D yes $node; done
$ for node in $GROUP; do gnt-node migrate -f --submit $node; done

after maintenance, the tags would be removed and the nodes undrained. chef's kiss, that's the whole loop 💅

🦋 Offline Rolling node reboot output 🦋

if all instances are shut down, usually larger node groups can be found. :

$ hroller --offline-maintenance -L
'Node Reboot Groups'
node1.example.com,node3.example.com,node5.example.com
node8.example.com,node6.example.com,node2.example.com
node7.example.com,node4.example.com

🍓 Rolling reboots with non-redundant instances 🍓

by default, hroller plans capacity to move the non-redundant instances out of the nodes to be rebooted. if requested, appropriate locations for the non-redundant instances can be shown. the assumption is that instances are moved back to their original node after each reboot; these back moves are not part of the output. :

$ hroller --print-moves -L
'Node Reboot Groups'
node-01-002,node-01-003
  inst-20 node-01-001
  inst-21 node-01-000
  inst-30 node-01-005
  inst-31 node-01-004
node-01-004,node-01-005
  inst-40 node-01-001
  inst-41 node-01-000
  inst-50 node-01-003
  inst-51 node-01-002
node-01-001,node-01-000
  inst-00 node-01-002
  inst-01 node-01-003
  inst-10 node-01-005
  inst-11 node-01-004

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🙈 REPORTING BUGS 🙈

report bugs to the project's issue tracker or contact the developers using the Ganeti mailing list. don't be shy, they're nice, fr fr 🫶

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⭐ SEE ALSO ⭐

Ganeti overview and specifications: ganeti(7) (general overview), ganeti-os-interface(7) (guest OS definitions), ganeti-extstorage-interface(7) (external storage providers).

Ganeti commands: gnt-cluster(8) (cluster-wide commands), gnt-job(8) (job-related commands), gnt-node(8) (node-related commands), gnt-instance(8) (instance commands), gnt-os(8) (guest OS commands), gnt-storage(8) (storage commands), gnt-group(8) (node group commands), gnt-backup(8) (instance import/export commands), gnt-debug(8) (debug commands).

Ganeti daemons: ganeti-watcher(8) (automatic instance restarter), ganeti-cleaner(8) (job queue cleaner), ganeti-noded(8) (node daemon), ganeti-rapi(8) (remote API daemon).

Ganeti htools: htools(1) (generic binary), hbal(1) (cluster balancer), hspace(1) (capacity calculation), hail(1) (IAllocator plugin), hscan(1) (data gatherer from remote clusters), hinfo(1) (cluster information printer), mon-collector(7) (data collectors interface).

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💜 COPYRIGHT 💜

okay so this next bit is the legal text and bestie I am not paraphrasing it — lawyers are the one fandom you don't remix. here it is, word for word: 👇

Copyright (C) 2006-2015 Google Inc. All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

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and that's the whole page, babe 💖 this one came from the Ganeti crew, she's HROLLER(1), running Version 3.1.0~rc2 — go forth, reboot responsibly, and don't be the person who reboots a primary and its secondary at the same time. we don't do that here. 🌸✨👑