[ClusterLabs] Rolling upgrade failure: v2.1.6 node cannot connect after upgrading peer to v3.0.1

[S Sathish S]

Hi Team,

Any update on below issue.

Thanks and Regards,
S Sathish S
From: S Sathish S
Sent: 09 February 2026 16:19
To: Cluster Labs - All topics related to open-source clustering welcomed <users at clusterlabs.org>
Cc: Devakumar K <devakumar.k at ericsson.com>
Subject: Rolling upgrade failure: v2.1.6 node cannot connect after upgrading peer to v3.0.1

Hi Team,

Issue : We are performing a rolling upgrade from Pacemaker v2.1.6 to v3.0.1 in a two-node cluster. According to the [Pacemaker 3.0 Changes documentation]( ⚡ Pacemaker 3.0 Changes<https://projects.clusterlabs.org/w/projects/pacemaker/pacemaker_3.0_changes/> ), rolling upgrades from Pacemaker 2.0.0 and later should be supported with minimal changes.

However, after upgrading the first node (Node 1) to Pacemaker 3.0.1, the second node (Node 2) running Pacemaker 2.1.6 is unable to connect to the cluster after reboot of node2. Pacemaker fails to start on Node 2 with the error:

Error: error running crm_mon, is pacemaker running?
  crm_mon: Connection to cluster failed: Connection refused

Expected Behaviour:
During a rolling upgrade, both nodes should remain operational and communicate with each other until the second node is upgraded. The non-upgraded node (2.1.6) should continue to function while the upgraded node (3.0.1) acts as DC.

Questions:
1. Is this a known limitation with the rolling upgrade path from 2.1.6 to 3.0.1?
2. Are there specific compatibility issues between Pacemaker 3.0.1 and 2.1.6 that prevent cluster communication?
3. Are there any additional logs or diagnostic information needed to troubleshoot this issue?

Environment:
- Cluster: 2-node RHEL 8 cluster with Corosync
- Node 1 (node1): Upgraded to Pacemaker 3.0.1-1.el8
- Node 2 (node2): Running Pacemaker 2.1.6-1.el8 (not yet upgraded)

Node 1 (node1) - Upgraded:
Pacemaker: 3.0.1-1.el8
Corosync: 3.1.10-1.el8
PCS: 0.12.2-1.el8
libknet1: 1.33-1.el8
resource-agents: 4.17.0-1.el8

Node 2 (node2) - Not Upgraded:
Pacemaker: 2.1.6-1.el8
Corosync: 3.1.7-1.el8
PCS: 0.10.19-2.el8
libknet1: 1.25-1.el8
resource-agents: 4.12.0-1.el8


Node1:
[root at node1 testadmin]# pcs status pcsd
  node1: Online
  node2: Online

[root at node1 testadmin]# pcs status
Cluster Summary:
  * Stack: corosync (Pacemaker is running)
  * Current DC: node1 (version 3.0.1-1.el8-3.0.1) - partition with quorum
  * Last updated: Sat Feb  7 11:39:00 2026 on node1
  * Last change:  Sat Feb  7 11:22:01 2026 by hacluster via hacluster on node1
  * 2 nodes configured
  * 23 resource instances configured (2 DISABLED)

Node List:
  * Online: [ node1 ]
  * OFFLINE: [ node2 ]

Full List of Resources:
  * SNMP_node2       (ocf:pacemaker:ClusterMon):      Stopped
  * SNMP_node1       (ocf:pacemaker:ClusterMon):      Started node1

Daemon Status:
  corosync: active/enabled
  pacemaker: active/enabled
  pcsd: active/enabled


[root at node1 testadmin]# rpm -qa |  egrep "pcs|pacemaker|corosy|pacemak|resource-a|libknet"
libknet1-1.33-1.el8.x86_64
libknet1-compress-lz4-plugin-1.33-1.el8.x86_64
libknet1-compress-zstd-plugin-1.33-1.el8.x86_64
libknet1-crypto-plugins-all-1.33-1.el8.x86_64
pacemaker-libs-3.0.1-1.el8.x86_64
pcs-0.12.2-1.el8.x86_64
corosynclib-3.1.10-1.el8.x86_64
libknet1-compress-bzip2-plugin-1.33-1.el8.x86_64
libknet1-compress-lzma-plugin-1.33-1.el8.x86_64
libknet1-compress-zlib-plugin-1.33-1.el8.x86_64
libknet1-compress-plugins-all-1.33-1.el8.x86_64
libknet1-crypto-openssl-plugin-1.33-1.el8.x86_64
libknet1-plugins-all-1.33-1.el8.x86_64
pacemaker-schemas-3.0.1-1.el8.noarch
pacemaker-cluster-libs-3.0.1-1.el8.x86_64
pacemaker-3.0.1-1.el8.x86_64
corosync-3.1.10-1.el8.x86_64
libknet1-compress-lzo2-plugin-1.33-1.el8.x86_64
libknet1-crypto-nss-plugin-1.33-1.el8.x86_64
resource-agents-4.17.0-1.el8.x86_64
pacemaker-cli-3.0.1-1.el8.x86_64
[root at node1 testadmin]#


Node2:
[root at node2 testadmin]# pcs status
Error: error running crm_mon, is pacemaker running?
  crm_mon: Connection to cluster failed: Connection refused

[root at node2 testadmin]# pcs status pcsd
  node2: Online
  node1: Online
[root at node2 testadmin]#

[root at node2 testadmin]# rpm -qa |  egrep "pcs|pacemaker|corosy|pacemak|resource-a|libknet"
libknet1-compress-bzip2-plugin-1.25-1.el8.x86_64
libknet1-compress-zlib-plugin-1.25-1.el8.x86_64
libknet1-crypto-openssl-plugin-1.25-1.el8.x86_64
pacemaker-schemas-2.1.6-1.el8.noarch
pacemaker-2.1.6-1.el8.x86_64
libknet1-1.25-1.el8.x86_64
corosync-3.1.7-1.el8.x86_64
libknet1-compress-lz4-plugin-1.25-1.el8.x86_64
libknet1-compress-lzo2-plugin-1.25-1.el8.x86_64
libknet1-compress-zstd-plugin-1.25-1.el8.x86_64
libknet1-crypto-nss-plugin-1.25-1.el8.x86_64
libknet1-crypto-plugins-all-1.25-1.el8.x86_64
resource-agents-4.12.0-1.el8.x86_64
pacemaker-libs-2.1.6-1.el8.x86_64
pacemaker-cli-2.1.6-1.el8.x86_64
pcs-0.10.19-2.el8.x86_64
corosynclib-3.1.7-1.el8.x86_64
libknet1-compress-lzma-plugin-1.25-1.el8.x86_64
libknet1-compress-plugins-all-1.25-1.el8.x86_64
libknet1-plugins-all-1.25-1.el8.x86_64
pacemaker-cluster-libs-2.1.6-1.el8.x86_64

Thanks and Regards,
S Sathish S
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