I am receiving timeout errors on my redis server I am using for session state with a webforms site on AzureApps

Hi Robert Woods
It sounds frustrating to encounter these sudden timeout errors with your Azure Redis server, especially without recent changes or traffic spikes. Since upgrading the service tier hasn’t resolved the issue, here are a few steps you can take to troubleshoot and potentially fix the problem:

1. Check Client-Side Configuration: The StackExchange.Redis.RedisTimeoutException during an EVAL command often points to client-side bottlenecks. Ensure your ConnectionMultiplexer is implemented as a singleton and reused across requests, as creating multiple instances can lead to contention. Also, consider increasing the SyncTimeout value (e.g., to 10000ms) in your connection string to give operations more time to complete: "your.redis.cache.windows.net:6380,password=...,ssl=True,abortConnect=False,syncTimeout=10000".
2. Review EVAL Script Performance: Since the timeout occurs during an EVAL command, the Lua script used for session state operations might be taking too long. Connect to your Redis instance using redis-cli and run the SLOWLOG GET command to check if the script’s execution time exceeds the 5000ms timeout. If it does, optimizing or simplifying the script could help.
3. Monitor Redis Metrics: Even without a traffic spike, check Azure Monitor for metrics like CPU usage, memory pressure, server load, and connected clients. High server load or memory fragmentation could cause delays. If memory usage is near the limit, setting a maxmemory-reserved value or clearing stale session data might free up resources.
4. ThreadPool Settings: The error stack trace might include ThreadPool stats (e.g., IOCP/WORKER busy threads). If the busy count exceeds the minimum, thread starvation could be an issue. In your WebForms app, try setting a higher minimum in Application_Start: System.Threading.ThreadPool.SetMinThreads(200, 200);.
5. Network Latency: Since you’re on App Service, ensure both the App Service and Redis instance are in the same Azure region to minimize latency. You can also test connectivity with redis-cli or PSPing to rule out network blips.

If these don’t resolve the issue, could you share more details from the stack trace (e.g., qs, in, IOCP, WORKER values)? That could pinpoint whether it’s a client, server, or network problem.

Timeout performing EVAL (10000ms), next: EVAL, inst: 22, qu: 0, qs: 0, aw: False, bw: SpinningDown, rs: ReadAsync, ws: Idle, in: 0, last-in: 0, cur-in: 0, sync-ops: 922, async-ops: 1, serverEndpoint: decisive-redis.redis.cache.windows.net:6380, conn-sec: 313.84, aoc: 0, mc: 1/1/0, mgr: 10 of 10 available, clientName: DW0LDWK000147(SE.Redis-v2.8.22.13109)(Microsoft.Web.RedisSessionStateProvider-v5.1.0.0), IOCP: (Busy=0,Free=1000,Min=4,Max=1000), WORKER: (Busy=9,Free=8182,Min=4,Max=8191), v: 2.8.22.13109 (Please take a look at this article for some common client-side issues that can cause timeouts: https://stackexchange.github.io/StackExchange.Redis/Timeouts)

Hi Robert Woods
(Azure Cache for Redis as your session state server for a WebForms site on App Service, no recent changes, no traffic spikes, and a tier upgrade that didn’t resolve it). I’d be happy to assist you in resolving this using insights from the Azure Redis troubleshooting guide.

The error ("Timeout performing EVAL (10000ms)") suggests that a Lua script—likely used by the Microsoft.Web.RedisSessionStateProvider for session updates—might be taking longer than expected. A 10-second timeout is fairly generous, so something seems to be slowing it down. Your ThreadPool appears healthy (with many free threads), and the server metrics don’t indicate an obvious overload. Since upgrading the tier didn’t help, it could be a subtle issue with the script or server behavior.

1. Examine the Lua Script: The EVAL command might be the key. If it’s processing large session data or performing complex tasks, it could exceed the timeout, even without extra traffic.
   • Enabling the Redis Slow Log to investigate? You could use CONFIG SET slowlog-log-slower-than 10000 and SLOWLOG GET 10 in a Redis client (perhaps with redis-cli or by contacting Azure support, as it’s not directly in the portal). If EVAL shows up as slow, we could explore optimizing it—perhaps it’s handling too many keys or large datasets. Since the session provider manages the script, a workaround might be needed if it’s intensive.
2. Review Server Performance: There’s a chance another operation is quietly delaying your EVAL, even without a traffic increase.
   • Checking the Azure Portal for Redis metrics like CPU, Server Load, and Connected Clients? If CPU or Server Load is unusually high, or if there’s an unexpected number of clients, that might point to the issue. Options like clustering (available with Premium tier) or limiting other clients via support could help if there’s interference.
3. Adjust the Client Settings: A small tweak to your app’s configuration might provide some relief and extra insight.
   • Updating your web.config to extend the timeout and add retries for the session provider? Here’s an example:

          <sessionState mode="Custom" customProvider="RedisSessionStateProvider"> <providers> 
          <add name="RedisSessionStateProvider"      type="Microsoft.Web.Redis.RedisSessionStateProvider"
          host="decisive-redis.redis.cache.windows.net" 
          port="6380"
          accessKey="your-key" 
          ssl="true" 
          operationTimeoutInMilliseconds="15000" <!-- Increased from 10000 --> connectionRetryCount="3" 
          connectionRetryTimeoutInMilliseconds="5000" /> ``
          </providers> 
          </sessionState>
          
     

   • Additionally, adding logging could help: in your global.asax.cs, you might include:

           Microsoft.Web.Redis.StackExchangeRedisEventSource.Log.Information += (msg) => System.Diagnostics.Trace.WriteLine(msg);
     

4. Consider Network Stability: A brief network issue between App Service and Redis could also be a factor, even in the same region.
   • Reviewing Connected Client Latency or Cache Latency in Azure Monitor? If you notice any spikes, placing both services in the same VNet (a Premium tier option) might improve consistency.

I’d kindly recommend starting with the Slow Log to see if the EVAL script is the holdup—it’s a quick way to narrow things down. Then, perhaps check the server metrics in the portal. Applying the web.config updates could give you more time and useful logs.

I would request you to refer the below mentioned links for more information
https://learn.microsoft.com/en-us/azure/redis/troubleshoot-timeouts?source=recommendations

I hope this information helps. Please do let us know if you have any further queries.

Hi Robert Woods
We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.