Description

The IP address of the Solr server gets cached on the .NET level. This behavior might lead to connection issues if the solr.search connection string value is a domain name instead of a static IP address. If the DNS mapping for the domain is changed to a new IP address, the changes are not picked up by Sitecore instances until the instances have been restarted.
This is a common scenario when using SearchStax Disaster Recovery. This article provides recommendations on how to reestablish connection to Solr when the DNS is updated to point to a new IP address.

Solution

To reestablish connection to Solr when the DNS is updated to point to a new IP address, consider one of the following options:

• For Sitecore XP 10.2.1 and later, enable the feature using the configuration file \App_Config\Include\Examples\Sitecore.ContentSearch.Solr.EnableConnectionLeaseTimeout.config.example.
• For Sitecore XP 10.2.0, download and install the latest cumulative hotfix as specified in KB1001439. Then enable the feature following the instructions from the \Documentation\Sitecore.Platform[.Cumulative].Instructions 10.2.x rev. xxxxxx PRE.md file.
• For Sitecore XP 10.0.1, download and install the corresponding cumulative hotfix available in KB1001334, and then enable the feature using the configuration file \App_Config\Include\Examples\Sitecore.ContentSearch.Solr.EnableConnectionLeaseTimeout.config.example.
• For Sitecore XP 10.0.0, download and install the corresponding cumulative hotfix available in KB1001333, and then enable the feature using the configuration file \App_Config\Include\Examples\Sitecore.ContentSearch.Solr.EnableConnectionLeaseTimeout.config.example.
• For Sitecore XP 9.3 and earlier, you can follow the customization steps. The cached result of the IP address resolved for a domain name can be removed periodically so that you do not have to manually restart Sitecore instances when the DNS mapping changes. Note that the code sample is given only as a starting point.
  
  1. Create the following class and build it into an assembly:

     using System;
     using System.Globalization;
     using HttpWebAdapters;
     using CommonServiceLocator;
     using Microsoft.Extensions.DependencyInjection;
     using Sitecore;
     using Sitecore.ContentSearch.SolrProvider.Abstractions;
     
     namespace YourNamespace
     {
         public class ResettableConnectionHttpWebRequestFactory : IHttpWebRequestFactory
         {
             private IHttpWebRequestFactory _httpWebRequestFactory;
             private readonly int _connectionLeaseTimeout;
             private static readonly TimeSpan DefaultConnectionLeaseTimeout = TimeSpan.FromMinutes(4);
     
             public ResettableConnectionHttpWebRequestFactory(string connectionLeaseTimeout)
             {
                 _connectionLeaseTimeout = (int)DateUtil.ParseTimeSpan(connectionLeaseTimeout, DefaultConnectionLeaseTimeout, CultureInfo.CurrentCulture)
                     .TotalMilliseconds;
             }
     
             public IHttpWebRequest Create(Uri url)
             {
                 var request = GetHttpWebRequestFactory().Create(url);
                 request.ServicePoint.ConnectionLeaseTimeout = _connectionLeaseTimeout;
     
                 return request;
             }
     
             private IHttpWebRequestFactory GetHttpWebRequestFactory()
             {
                 if (_httpWebRequestFactory != null)
     
                     return _httpWebRequestFactory;
     
                 return _httpWebRequestFactory = CreateHttpWebRequestFactory();
             }
     
             private IHttpWebRequestFactory CreateHttpWebRequestFactory()
             {
                 IHttpWebRequestFactory resultFactory;
     
                 var solrAddress = ServiceLocator.Current.GetService<BaseSolrSpecificSettings>().SolrAddress();
     
                 if (solrAddress != null && solrAddress.UseBaseAuthentication)
                 {
                     resultFactory =
                         new BasicAuthHttpWebRequestFactory(solrAddress.Username, solrAddress.Password);
                 }
                 else
                 {
                     resultFactory = new HttpWebRequestFactory();
                 }
     
                 return resultFactory;
             }
         }
     }

     Note: Add references to the following assemblies used by Sitecore:
     
     • CommonServiceLocator
     • Microsoft.Extensions.DependencyInjection
     • Microsoft.Extensions.DependencyInjection.Abstractions
     • Sitecore.ContentSearch
     • Sitecore.ContentSearch.SolrProvider
     • Sitecore.Kernel
     • SolrNet
  2. Put the assembly in the \bin folder of the website.
  3. Reference the class from the configuration by creating a configuration patch file in the \App_Config\Include\zzz folder:

     <?xml version="1.0" encoding="utf-8"?>
     <configuration xmlns:patch="http://www.sitecore.net/xmlconfig/" xmlns:role="http://www.sitecore.net/xmlconfig/role/" xmlns:search="http://www.sitecore.net/xmlconfig/search/">
       <sitecore search:require="solr">
         <contentSearch>
           <indexConfigurations>
             <solrHttpWebRequestFactory type="YourNamespace.ResettableConnectionHttpWebRequestFactory, YourDll">
               <param desc="connectionLeaseTimeout">00:03:00</param>
             </solrHttpWebRequestFactory>
           </indexConfigurations>
         </contentSearch>
       </sitecore>
     </configuration>

• To get a solution for other releases, contact Sitecore Support.