Synchronise 2026.1 with upstream#895
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The libvirt daemon ships with max_workers=20 and max_client_requests=5. Those defaults suit a multi-tenant host serving many mutually distrustful clients, where the per-client request cap protects the daemon from any single client monopolising it. Under Kolla-Ansible, nova-compute is effectively the sole privileged client of libvirtd, so the cap of 5 concurrent requests per client becomes the binding constraint rather than a safety net. When several instances build at once -- as they do during the tempest run of the upgrade jobs -- nova-compute's concurrent libvirt RPCs (instance defineXML calls plus the resource-tracker periodic) exceed five. Further requests queue, the connection's keepalive responses are starved, and after keepalive_interval (5s) x keepalive_count (5) = 25s libvirtd closes the connection. nova then sees "Cannot recv data: Input/output error" mid-defineXML, the build is rescheduled, and once all hosts are exhausted the instance is left in ERROR. This presents as flaky upgrade-job failures. Example failure, on the voting kolla-ansible-debian-bookworm-upgrade job (stable/2025.2): https://zuul.opendev.org/t/openstack/build/73ff5a97567d4e05b1774170e0f4aada with primary/logs/kolla/libvirt/libvirtd.txt showing libvirt's own recommendation to tune this parameter: warning : Client hit max requests limit 5. This may result in keep-alive timeouts. Consider tuning the max_client_requests server parameter ... error : connection closed due to keepalive timeout Raise the per-client cap to 20 -- comfortably above the handful of concurrent builds plus periodics seen in practice -- and the worker pool to 50 so that lifting the per-client limit does not starve other connections such as live migration, health checks and periodic tasks. Both values are exposed as variables (libvirt_max_client_requests and libvirt_max_workers) so operators can tune them further. This is not a Kolla-specific workaround -- the stock libvirtd.conf comment warns that setting max_client_requests too low "may cause keepalive timeouts", and since 2022 libvirtd emits the runtime warning quoted above. As Daniel Berrange explained when he added that warning, the keepalive packets "are subject to the 'max_client_requests' limit just like any API calls", so a client that saturates the limit can have its connection dropped: https://lists.libvirt.org/archives/list/devel@lists.libvirt.org/message/5NIJPA7SJVY55VSK7RTEDEHKWOZYJKT6/ Red Hat documents the same tuning for libvirt hosts under load in its knowledge base, notably "Too many active clients are dropping the connection" at https://access.redhat.com/solutions/28146. Assisted-By: Claude Opus 4.8 (1M context, medium effort) Partial-Bug: 2158515 Change-Id: I131c3d4d57dc73ca4dd421cc8f28465248c9830e (cherry picked from commit 5acd2f9) Signed-off-by: Michael Still <mikal@stillhq.com>
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Alex-Welsh
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Jul 6, 2026
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This PR contains a snapshot of 2026.1 from upstream stable/2026.1.