Is there any way to check the solr is running in sitecore

Question

We have requirement to redirect to a error page if the solr is stopped programtically in sitecore. Is there any way to check whether the solr is running or not?

Answer 1

I hope you are asking about how to do it under sitecore services and so on. So if yes, use it:

var solrConnector = ServiceLocator.Current.GetInstance<ISolrConnector>();
if (solrConnector.IsOnline)
{
   //your code
}

Answer 2

If the Solr search service is not available when you run a query, the search provider produces a result similar to the result you get when you run a LINQ query against an empty collection. For example, the following query normally returns an array with at leat one element:

var result = context.GetQueryable<SearchResultItem>()
.Where(it => it.Content == "sitecore").ToArray();

However, if the Solr instance is not available when you run the query, the query returns an empty array. The same happens for other LINQ methods, such as .First():

var result = context.GetQueryable<SearchResultItem>()
 .Where(it => it.Content == "sitecore").First();

Normally, this query returns a first element that matches the search query. However, if the Solr instance is not available when you run the query, the query raises the InvalidOperationException("Sequence contains no elements.") exception. This is the standard behavior of the First() method with an empty result.

To find out if the Solr search service is not available: Pass an instance of the ThrowOnErrorExecutionContext execution context to the following query:

var result = context.GetQueryable<SearchResultItem>(new ThrowOnErrorExecutionContext())
.Where(it => it.Content == "sitecore").ToArray();

When you apply the ThrowOnErrorExecutionContext context to the query, the LINQ query returns results as in the previous examples under normal conditions. However, if the Solr instance is not available, the search provider throws a SearchServiceUnavailableException exception that you can catch and handle:

var queryable = context.GetQueryable<SearchResultItem>(new ThrowOnErrorExecutionContext());
try
{
var result = queryable.Where(it => it.Content == "sitecore").ToArray();
}
catch (SearchServiceUnavailableException ex)
{
// Handle unavailable search service 
}  

Another way to check if Solr is running is to use the Solr ping API. The ping API is a simple way to check if Solr is running by sending a ping request to the Solr server. Here's an example

var solrUrl = "http://localhost:8983/solr/admin/ping?wt=json";

using (var client = new HttpClient())
{
    try
    {
        var response = await client.GetAsync(solrUrl);
        response.EnsureSuccessStatusCode();
        // Solr is running, continue processing
    }
    catch (HttpRequestException ex)
    {
        // Solr is not running, redirect to error page
        Response.Redirect("/error.aspx");
    }
}