dotnet/yarp · error · InvalidOperationException

Session affinity is disabled for cluster.

Error message

Session affinity is disabled for cluster.

What it means

Thrown by BaseEncryptedSessionAffinityPolicy.AffinitizeResponse when `config.Enabled` is not true (null or false). AffinitizeResponse writes the affinity key to the response, which is only meaningful when affinity is enabled; calling it on a disabled cluster is a programming/config error.

Source

Thrown at src/ReverseProxy/SessionAffinity/BaseEncryptedSessionAffinityPolicy.cs:34

{
    private readonly IDataProtector _dataProtector;
    protected static readonly object AffinityKeyId = new object();
    protected readonly ILogger Logger;

    protected BaseEncryptedSessionAffinityPolicy(IDataProtectionProvider dataProtectionProvider, ILogger logger)
    {
        ArgumentNullException.ThrowIfNull(logger);
        _dataProtector = dataProtectionProvider?.CreateProtector(GetType().FullName!) ?? throw new ArgumentNullException(nameof(dataProtectionProvider));
        Logger = logger;
    }

    public abstract string Name { get; }

    public void AffinitizeResponse(HttpContext context, ClusterState cluster, SessionAffinityConfig config, DestinationState destination)
    {
        if (!config.Enabled.GetValueOrDefault())
        {
            throw new InvalidOperationException($"Session affinity is disabled for cluster.");
        }

        if (context.RequestAborted.IsCancellationRequested)
        {
            // Avoid wasting time if the client is already gone.
            return;
        }

        // Affinity key is set on the response only if it's a new affinity.
        if (!context.Items.ContainsKey(AffinityKeyId))
        {
            var affinityKey = GetDestinationAffinityKey(destination);
            SetAffinityKey(context, cluster, config, affinityKey);
        }
    }

    public virtual AffinityResult FindAffinitizedDestinations(HttpContext context, ClusterState cluster, SessionAffinityConfig config, IReadOnlyList<DestinationState> destinations)
    {

View on GitHub (pinned to bd11867bee)

Solutions

1. Set `SessionAffinity.Enabled = true` on the cluster config that uses an encrypted affinity policy (Cookie).
2. Guard the call site: only invoke AffinitizeResponse when `config.Enabled.GetValueOrDefault()` is true.
3. Verify the cluster's SessionAffinityConfig is the one you intend (check config binding).

Example fix

// before
new ClusterConfig { SessionAffinity = new SessionAffinityConfig { AffinityKeyName = "Yarp.Affinity" } };
// after
new ClusterConfig { SessionAffinity = new SessionAffinityConfig { Enabled = true, AffinityKeyName = "Yarp.Affinity" } };

if (!config.Enabled.GetValueOrDefault())
    throw new InvalidOperationException("Enable SessionAffinity before calling AffinitizeResponse.");

static bool AffinityEnabled(SessionAffinityConfig? config) =>
    config is not null && config.Enabled.GetValueOrDefault();

When it happens

Trigger: The affinity policy's AffinitizeResponse is invoked on a cluster whose SessionAffinityConfig.Enabled is false or unset. Typically happens when the policy is wired but the cluster config did not enable affinity.

Common situations: Custom middleware or a test harness calls AffinitizeResponse directly. Cluster config partially migrated: policy registered but `SessionAffinity:Enabled` omitted. Config binding defaults Enabled to null.

Related errors

• Session affinity is disabled for cluster {cluster.ClusterId}
• Session affinity is disabled for cluster.
• Session affinity is disabled for cluster {cluster.ClusterId}
• Unknown transform: {string.Join(';', rawTransform.Keys)}
• The transform contains more parameters than expected: {strin

AI-assisted analysis of dotnet/yarp@bd11867bee (2026-08-13). Data as JSON: /api/errors/05682ddf52c57937. Report an issue: GitHub.