Error while rebuilding the search index on Sitecore 8.2 and Solr 6.6.1

Question

We are able to successfully build all the indexes for the first time except sitecore_master_index, sitecore_web_index and Sitecore_core_index

And when trying to rebuild sitecore_master_index for the first time, getting error as mentioned https://community.sitecore.net/general/f/11/t/8902

Already implemented the solution posted on above question. But now getting a different exception while rebuilding as mentioned below:

Job started: Index_Update_IndexName=sitecore_master_index|#
Exception: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. 
---> SolrNet.Exceptions.SolrConnectionException: 
    <?xml version="1.0" encoding="UTF-8"?>
    <response>
        <lst name="responseHeader">
            <int name="status">400</int>
            <int name="QTime">1</int>
        </lst>
        <lst name="error">
            <lst name="metadata">
                <str name="error-class">org.apache.solr.common.SolrException</str>
                <str name="root-error-class">org.apache.solr.common.SolrException</str>
            </lst>
            <str name="msg">Solr instance is not running in SolrCloud mode.</str>
            <int name="code">400</int>
        </lst>
    </response>
 ---> 
System.Net.WebException: The remote server returned an error: (400) Bad Request.
   at System.Net.HttpWebRequest.GetResponse()
   at HttpWebAdapters.Adapters.HttpWebRequestAdapter.GetResponse()
   at SolrNet.Impl.SolrConnection.GetResponse(IHttpWebRequest request)
   at SolrNet.Impl.SolrConnection.Get(String relativeUrl, IEnumerable 1 parameters)
   --- End of inner exception stack trace ---
   at SolrNet.Impl.SolrConnection.Get(String relativeUrl, IEnumerable 1 parameters)
   at SolrNet.Impl.SolrCoreAdmin.SendAndParseHeader(ISolrCommand cmd)
   at Sitecore.ContentSearch.SolrProvider.SwitchOnRebuildSolrCloudSearchIndex.CreateAlias(String aliasName, String collection)
   at Sitecore.ContentSearch.SolrProvider.SwitchOnRebuildSolrCloudSearchIndex.SetAlias(String aliasName, String collection)
   at Sitecore.ContentSearch.SolrProvider.SwitchOnRebuildSolrCloudSearchIndex.SetAliasesConfiguration()
   at Sitecore.ContentSearch.SolrProvider.SwitchOnRebuildSolrCloudSearchIndex.Rebuild(Boolean resetIndex, Boolean optimizeOnComplete)
   --- End of inner exception stack trace ---
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at Sitecore.Reflection.ReflectionUtil.InvokeMethod(MethodInfo method, Object[] parameters, Object obj)
   at Sitecore.Jobs.JobRunner.RunMethod(JobArgs args)
   at (Object , Object[] )
   at Sitecore.Pipelines.CorePipeline.Run(PipelineArgs args)
   at Sitecore.Pipelines.DefaultCorePipelineManager.Run(String pipelineName, PipelineArgs args, String pipelineDomain)
   at Sitecore.Jobs.Job.ThreadEntry(Object state)

Please suggest what to do?

Thanks

Answer 1

The issue is now resolved, actually by mistake we enabled Sitecore.ContentSearch.SolrCloud.SwitchOnRebuild.config.example and after disabling it again indexes rebuild successfully.

Answer 2

For me, the solution was obvious once I reviewed the Solr error logs. I was quickly able to see that one of my switch-on-rebuild collections was missing. Creating the missing collection solved the problem.