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<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;color:#1F497D;mso-fareast-language:EN-US">Hi!<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;color:#1F497D;mso-fareast-language:EN-US">Please forgive me for asking AI; anyway here is what AI suggested:<o:p></o:p></span></p>
<p class="MsoNormal"><b><span lang="EN-US" style="font-size:11.0pt;color:#1F497D;mso-fareast-language:EN-US">Quick clarification (Alice)<o:p></o:p></span></b></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;color:#1F497D;mso-fareast-language:EN-US">I need the environment details to give precise guidance:<o:p></o:p></span></p>
<ul style="margin-top:0cm" type="disc">
<li class="MsoNormal" style="color:#1F497D;mso-list:l5 level1 lfo1"><span style="font-size:11.0pt;mso-fareast-language:EN-US">Linux distro and kernel version<o:p></o:p></span></li><li class="MsoNormal" style="color:#1F497D;mso-list:l5 level1 lfo1"><span style="font-size:11.0pt;mso-fareast-language:EN-US">Corosync and Pacemaker versions<o:p></o:p></span></li><li class="MsoNormal" style="color:#1F497D;mso-list:l5 level1 lfo1"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Network topology (dedicated heartbeat VLAN vs shared LAN) and link types (1GbE/10GbE)<o:p></o:p></span></li><li class="MsoNormal" style="color:#1F497D;mso-list:l5 level1 lfo1"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Cluster size (nodes count) and the resources being failed over<o:p></o:p></span></li><li class="MsoNormal" style="color:#1F497D;mso-list:l5 level1 lfo1"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Do you control MTU, switches, and can you run multicast/UDPU or prefer TCP? Please provide those three essentials first:
device/software+versions, error frequency (always/sometimes), any recent changes.<o:p></o:p></span></li></ul>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;color:#1F497D;mso-fareast-language:EN-US">Below I assume a generic production setup (modern Corosync 3.x and Pacemaker 2.x on Linux).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D;mso-fareast-language:EN-US">Short answers<o:p></o:p></span></p>
<ol style="margin-top:0cm" start="1" type="1">
<li class="MsoNormal" style="color:#1F497D;mso-list:l1 level1 lfo2"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Yes — sub‑second detection and initiation can be achieved in production with modern Corosync/Pacemaker, but only with
careful tuning, dedicated low‑latency networking, and acceptance of trade‑offs.<o:p></o:p></span></li><li class="MsoNormal" style="color:#1F497D;mso-list:l1 level1 lfo2"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Community reports and measurements vary: stable failovers of ~200–700 ms have been reported for simple resources; 1s is
a commonly cited reliable minimum in real deployments. Expect full resource recovery often to be longer (seconds) depending on service stop/start times.<o:p></o:p></span></li><li class="MsoNormal" style="color:#1F497D;mso-list:l1 level1 lfo2"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Yes — post‑2015 releases improved messaging stacks, lower‑latency transports (UDPU improvements and CPR/TSN work), better
quorum/stonith handling, and more tunable timeouts that reduce detection latency.<o:p></o:p></span></li><li class="MsoNormal" style="color:#1F497D;mso-list:l1 level1 lfo2"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Key params and trade‑offs are listed below.<o:p></o:p></span></li></ol>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;color:#1F497D;mso-fareast-language:EN-US">Quick Fix (try first, <2 minutes)<o:p></o:p></span></p>
<ul style="margin-top:0cm" type="disc">
<li class="MsoNormal" style="color:#1F497D;mso-list:l6 level1 lfo3"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Ensure cluster network has low jitter and packet loss (ping <1 ms on dedicated link).
</span><span style="font-size:11.0pt;mso-fareast-language:EN-US">Confirm with: ping -i 0.1 for sample jitter.<o:p></o:p></span></li><li class="MsoNormal" style="color:#1F497D;mso-list:l6 level1 lfo3"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Verify corosync/pacemaker versions: corosync -v ; pcs --version (or pacemaker --version).
</span><span style="font-size:11.0pt;mso-fareast-language:EN-US">Report results. (</span><span style="font-size:11.0pt;font-family:"Segoe UI Emoji",sans-serif;mso-fareast-language:EN-US">✅</span><span style="font-size:11.0pt;mso-fareast-language:EN-US"> or
</span><span style="font-size:11.0pt;font-family:"Segoe UI Emoji",sans-serif;mso-fareast-language:EN-US">❌</span><span style="font-size:11.0pt;mso-fareast-language:EN-US">)<o:p></o:p></span></li></ul>
<p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D;mso-fareast-language:EN-US">Moderate steps (~5 minutes)<o:p></o:p></span></p>
<ol style="margin-top:0cm" start="1" type="1">
<li class="MsoNormal" style="color:#1F497D;mso-list:l0 level1 lfo4"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Use dedicated heartbeat network (separate VLAN/interface) and set proper MTU.<o:p></o:p></span></li><li class="MsoNormal" style="color:#1F497D;mso-list:l0 level1 lfo4"><span style="font-size:11.0pt;mso-fareast-language:EN-US">Tune Corosync:<o:p></o:p></span>
<ul style="margin-top:0cm" type="disc">
<li class="MsoNormal" style="color:#1F497D;mso-list:l0 level2 lfo4"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">transport: use udp (UDPU) or the recommended transport for your version.<o:p></o:p></span></li><li class="MsoNormal" style="color:#1F497D;mso-list:l0 level2 lfo4"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">token and consensus timeouts (example conservative starting point for sub‑second):<o:p></o:p></span>
<ul style="margin-top:0cm" type="disc">
<li class="MsoNormal" style="color:#1F497D;mso-list:l0 level3 lfo4"><span style="font-size:11.0pt;mso-fareast-language:EN-US">token: 500 (ms)<o:p></o:p></span></li><li class="MsoNormal" style="color:#1F497D;mso-list:l0 level3 lfo4"><span style="font-size:11.0pt;mso-fareast-language:EN-US">token_timeout: 1000 (ms)<o:p></o:p></span></li><li class="MsoNormal" style="color:#1F497D;mso-list:l0 level3 lfo4"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">join/consensus timeouts: reduce join and hold timers modestly<o:p></o:p></span></li></ul>
</li><li class="MsoNormal" style="color:#1F497D;mso-list:l0 level2 lfo4"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">For Corosync 3.x, tune rrm and cpusets per docs (exact param names depend on version).<o:p></o:p></span></li></ul>
</li><li class="MsoNormal" style="color:#1F497D;mso-list:l0 level1 lfo4"><span style="font-size:11.0pt;mso-fareast-language:EN-US">Pacemaker timeouts:<o:p></o:p></span>
<ul style="margin-top:0cm" type="disc">
<li class="MsoNormal" style="color:#1F497D;mso-list:l0 level2 lfo4"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">cluster property stonith-enabled=true (ensure fencing is fast)<o:p></o:p></span></li><li class="MsoNormal" style="color:#1F497D;mso-list:l0 level2 lfo4"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">set stonith-timeout and migration-thresholds to low safe values<o:p></o:p></span></li><li class="MsoNormal" style="color:#1F497D;mso-list:l0 level2 lfo4"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">resource agent timeouts: set op monitor intervals to 200–500ms for services that support fast probes<o:p></o:p></span></li></ul>
</li><li class="MsoNormal" style="color:#1F497D;mso-list:l0 level1 lfo4"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Use lightweight health checks (fast monitors) rather than heavy scripts.<o:p></o:p></span></li><li class="MsoNormal" style="color:#1F497D;mso-list:l0 level1 lfo4"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Test failovers under load and measure with timestamps in logs (corosync/pacemaker logs include timing).<o:p></o:p></span></li></ol>
<p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D;mso-fareast-language:EN-US">Nuclear option<o:p></o:p></span></p>
<ul style="margin-top:0cm" type="disc">
<li class="MsoNormal" style="color:#1F497D;mso-list:l4 level1 lfo5"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">If tuning cannot reach target, consider redesign: split services into smaller failover units, use active‑active instead
of active‑passive, or replace with specialized low‑latency HA solutions. </span>
<span style="font-size:11.0pt;mso-fareast-language:EN-US">Back up configs and data before any disruptive changes.<o:p></o:p></span></li></ul>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;color:#1F497D;mso-fareast-language:EN-US">Concrete example (decisive, reasonable defaults)<o:p></o:p></span></p>
<ul style="margin-top:0cm" type="disc">
<li class="MsoNormal" style="color:#1F497D;mso-list:l7 level1 lfo6"><span style="font-size:11.0pt;mso-fareast-language:EN-US">corosync.conf (illustrative):<o:p></o:p></span>
<ul style="margin-top:0cm" type="disc">
<li class="MsoNormal" style="color:#1F497D;mso-list:l7 level2 lfo6"><span style="font-size:11.0pt;mso-fareast-language:EN-US">token: 500<o:p></o:p></span></li><li class="MsoNormal" style="color:#1F497D;mso-list:l7 level2 lfo6"><span style="font-size:11.0pt;mso-fareast-language:EN-US">token_timeout: 1000<o:p></o:p></span></li><li class="MsoNormal" style="color:#1F497D;mso-list:l7 level2 lfo6"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">interface mcast/udpu with bindnetaddr on dedicated NIC<o:p></o:p></span></li></ul>
</li><li class="MsoNormal" style="color:#1F497D;mso-list:l7 level1 lfo6"><span style="font-size:11.0pt;mso-fareast-language:EN-US">Pacemaker resource monitor ops:<o:p></o:p></span>
<ul style="margin-top:0cm" type="disc">
<li class="MsoNormal" style="color:#1F497D;mso-list:l7 level2 lfo6"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">op monitor interval="300ms" timeout="1500ms"<o:p></o:p></span></li></ul>
</li><li class="MsoNormal" style="color:#1F497D;mso-list:l7 level1 lfo6"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Ensure fencing/stonith completes in <500ms (fast power fencing or virtualized APi).<o:p></o:p></span></li></ul>
<p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D;mso-fareast-language:EN-US">Trade-offs and risks<o:p></o:p></span></p>
<ul style="margin-top:0cm" type="disc">
<li class="MsoNormal" style="color:#1F497D;mso-list:l2 level1 lfo7"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">False positives: aggressive timeouts increase split‑brain/failover storm risk.
</span><span style="font-size:11.0pt;mso-fareast-language:EN-US">Require rock‑solid network and reliable fencing.<o:p></o:p></span></li><li class="MsoNormal" style="color:#1F497D;mso-list:l2 level1 lfo7"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Network sensitivity: jitter/packet loss will cause spurious failovers.
</span><span style="font-size:11.0pt;mso-fareast-language:EN-US">Dedicated link and QoS recommended.<o:p></o:p></span></li><li class="MsoNormal" style="color:#1F497D;mso-list:l2 level1 lfo7"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">CPU/network overhead: frequent heartbeats and fast monitors increase CPU/network usage (generally small, but measurable
on constrained nodes).<o:p></o:p></span></li><li class="MsoNormal" style="color:#1F497D;mso-list:l2 level1 lfo7"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Recovery time vs detection: detection can be sub‑second, but service stop/start and client reconnection often dominate
total outage.<o:p></o:p></span></li></ul>
<p class="MsoNormal"><span style="font-size:11.0pt;color:#1F497D;mso-fareast-language:EN-US">Reliable minimum recommendation<o:p></o:p></span></p>
<ul style="margin-top:0cm" type="disc">
<li class="MsoNormal" style="color:#1F497D;mso-list:l3 level1 lfo8"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">For production, target ~500 ms detection/initiation as an aggressive but achievable baseline; 1 s is safer and widely
reliable. </span><span style="font-size:11.0pt;mso-fareast-language:EN-US">Validate with end‑to‑end tests for your services.<o:p></o:p></span></li></ul>
<div style="mso-element:para-border-div;border:none;border-bottom:solid windowtext 1.0pt;padding:0cm 0cm 1.0pt 0cm">
<p class="MsoNormal" style="border:none;padding:0cm"><span lang="EN-US" style="font-size:11.0pt;color:#1F497D;mso-fareast-language:EN-US">If you want, provide the environment details I asked for and I’ll produce a tuned corosync.conf, pacemaker properties,
concrete resource monitor examples, and a test plan with log commands and expected timestamps.<o:p></o:p></span></p>
</div>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;color:#1F497D;mso-fareast-language:EN-US">As always: Take AI answers with a grain of salt
</span><span lang="EN-US" style="font-size:11.0pt;font-family:"Segoe UI Emoji",sans-serif;color:#1F497D;mso-fareast-language:EN-US">😉</span><span lang="EN-US" style="font-size:11.0pt;color:#1F497D;mso-fareast-language:EN-US"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Kind regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Ulrich Windl<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> Users <users-bounces@clusterlabs.org>
<b>On Behalf Of </b>Holger Haidinger <DE ERL SWD EM> via Users<br>
<b>Sent:</b> Friday, February 20, 2026 4:41 PM<br>
<b>To:</b> users@clusterlabs.org<br>
<b>Cc:</b> Holger Haidinger <DE ERL SWD EM> <Holger.Haidinger@fluenceenergy.com><br>
<b>Subject:</b> [EXT] [EXT] [ClusterLabs] Sub-second failover detection in Corosync/Pacemaker clusters - 2026 update?<o:p></o:p></span></p>
</div>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="background:#FFCCCB"><strong><span style="font-size:10.5pt;font-family:"Arial",sans-serif;color:black">Notice:</span></strong><span style="font-size:10.5pt;font-family:"Arial",sans-serif;color:black"> This email appears to be suspicious.
Do not trust the information, links, or attachments in this email without verifying the source through a trusted method. For more information see:
<a href="https://aka.ms/ProtectYourselfFromPhishing">https://aka.ms/ProtectYourselfFromPhishing</a><o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<div style="mso-element:para-border-div;border:solid black 1.0pt;padding:0cm 0cm 0cm 0cm;background:#FFF3CD">
<p style="background:#FFF3CD;border:none;padding:0cm"><span style="font-size:9.0pt;font-family:"Arial",sans-serif;color:black">Sicherheits-Hinweis: Diese E-Mail wurde von einer Person außerhalb des UKR gesendet. Seien Sie vorsichtig vor gefälschten Absendern,
wenn Sie auf Links klicken, Anhänge öffnen oder weitere Aktionen ausführen, bevor Sie die Echtheit überprüft haben.</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="color:black">Hi everyone,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:black">I'm revisiting a thread from 2015 (https://www.mail-archive.com/users@clusterlabs.org/msg00554.html) about achieving sub-second failover detection in HA clusters, and I'm curious about the current state of affairs
nearly a decade later.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:black">My Environment:<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:black">- Corosync 3.1.6<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black">- Pacemaker 2.1.2 <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black">- Architecture: 2-node cluster + QDevice (also testing 3-node setups)<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black">- Network: Dedicated physical NIC for cluster traffic (low-latency requirements)<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:black">Specific Questions:<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:black">1. With modern Corosync/Pacemaker versions, is sub-second fault detection and failover initiation realistically achievable in production environments?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black">2. Are there any published measurements or community experiences showing the fastest stable failover times you've achieved? What's considered a reliable minimum time span?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black">3. Have there been significant enhancements in the newer versions of Corosync and Pacemaker (post-2015) that specifically target detection speed and failover latency?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black">4. If sub-second detection is possible, what are the key configuration parameters and potential trade-offs (false positives, network sensitivity, resource overhead)?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:black">Thanks in advance!<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:black">Holger Haidinger<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
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