TechnitiumSoftware/DnsServer · warning · DnsServerException

Failed to resync configuration: only Secondary nodes can syn

Error message

Failed to resync configuration: only Secondary nodes can sync configuration from Primary nodes.

What it means

Thrown by TriggerResyncForConfig when GetPrimaryNode().State == ClusterNodeState.Self: this server is the primary. Like the refresh variant (192), resync pulls config from an upstream primary, which a primary node does not have. The guard stops the primary from attempting to resync from itself.

Source

Thrown at DnsServerCore/Cluster/ClusterManager.cs:1627

            ClusterNode primaryNode = GetPrimaryNode();

            if (primaryNode.State == ClusterNodeState.Self)
                throw new DnsServerException("Failed to refresh configuration: only Secondary nodes can sync configuration from Primary nodes.");

            TriggerRefreshForConfig(CONFIG_REFRESH_TIMER_INTERVAL, configRefreshIncludeZones);
        }

        public void TriggerResyncForConfig()
        {
            //do validation
            if (!ClusterInitialized)
                throw new DnsServerException("Failed to resync configuration: the Cluster is not initialized.");

            ClusterNode primaryNode = GetPrimaryNode();

            if (primaryNode.State == ClusterNodeState.Self)
                throw new DnsServerException("Failed to resync configuration: only Secondary nodes can sync configuration from Primary nodes.");

            _configLastSynced = DateTime.UnixEpoch; //to ensure complete config resync

            //trigger immediate config refresh
            TriggerRefreshForConfig(0);
        }

        private void TriggerRefreshForConfig(int refreshInterval, IReadOnlyCollection<string> configRefreshIncludeZones = null)
        {
            _configRefreshLock.Wait();
            try
            {
                if (configRefreshIncludeZones is not null)
                {
                    if (_configRefreshIncludeZones is null)
                        _configRefreshIncludeZones = configRefreshIncludeZones;
                    else
                        _configRefreshIncludeZones = [.. _configRefreshIncludeZones, .. configRefreshIncludeZones];

View on GitHub (pinned to d0484b6c1e)

Solutions

Call TriggerResyncForConfig only from Secondary nodes.
Branch shared automation on GetPrimaryNode().State and skip resync on the primary.
Disable the resync action in the UI when the current node is the primary.

Example fix

// before
clusterManager.TriggerResyncForConfig();

// after
if (clusterManager.GetPrimaryNode().State == ClusterNodeState.Self)
    return Ok("Primary node; nothing to resync.");
clusterManager.TriggerResyncForConfig();

Defensive patterns

Strategy: validation

Validate before calling

if (clusterManager.GetPrimaryNode().State == ClusterNodeState.Self)
    return Ok("Primary node; nothing to resync.");
clusterManager.TriggerResyncForConfig();

Type guard

static bool CanResyncFromPrimary(ClusterManager cm)
    => cm.ClusterInitialized && cm.GetPrimaryNode().State != ClusterNodeState.Self;

Try / catch

try { clusterManager.TriggerResyncForConfig(); }
catch (DnsServerException ex) when (ex.Message.Contains("only Secondary nodes can sync"))
{ /* primary node; no-op */ }

Prevention

Call resync only from secondaries.
Branch automation on node role to skip resync on the primary.
Resync is heavyweight (full pull) — confirm the node is a secondary first.

When it happens

Trigger: Calling TriggerResyncForConfig on the primary node of the cluster.

Common situations: Logged into the primary when clicking 'resync config from primary'; automation runs the resync job on all cluster members including the primary.

Related errors

AI-assisted analysis of TechnitiumSoftware/DnsServer@d0484b6c1e (2026-08-13). Data as JSON: /api/errors/1e20ea031a758fce. Report an issue: GitHub.