Could not load type '' from assembly 'Elasticsearch.Net, Version=7.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d'.

[felipedrumond]

I'm encountering an intermittent issue in a C# API that appears related to Elasticsearch.NET. Despite having multiple instances of the same build running in Kubernetes, when the error happens it only affects one pod—and even then, not all requests to that pod fail. Roughly 40% of the requests result in the following exception.

The fact that only 40% of the requests fail and not 100% might be explained by the nature of the queries being made, since there are a huge variety of them which would result in different code paths and elastic search queries being generated.

The exception bellow has innermostMethod Elasticsearch.Net.Nest_IHasChildQueryFormatter16.Serialize but I've seem others too:

Elasticsearch.Net.Nest_IHasChildQueryFormatter16.Serialize: 15971 cases
Elasticsearch.Net.Nest_IHasChildQueryFormatter16..ctor: 6480 cases
Elasticsearch.Net.Nest_IAggregationContainerFormatter2.Serialize: 657 cases
Elasticsearch.Net.Nest_IDateRangeQueryFormatter10.Serialize: 3699 cases

problemId System.TypeLoadException at Elasticsearch.Net.Nest_IHasChildQueryFormatter16.Serialize
type System.TypeLoadException
assembly Elasticsearch.Net.DynamicObjectResolverAllowPrivateFalseExcludeNullTrueNameMutateCamelCase, Version=0.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d
method Elasticsearch.Net.Nest_IHasChildQueryFormatter16.Serialize
outerType Elasticsearch.Net.UnexpectedElasticsearchClientException
outerMessage Could not load type '' from assembly 'Elasticsearch.Net, Version=7.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d'.
outerAssembly Elasticsearch.Net, Version=7.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d
outerMethod Elasticsearch.Net.Transport1+<RequestAsync>d__151.MoveNext
innermostType System.TypeLoadException
innermostMessage Could not load type '' from assembly 'Elasticsearch.Net, Version=7.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d'.
innermostAssembly Elasticsearch.Net.DynamicObjectResolverAllowPrivateFalseExcludeNullTrueNameMutateCamelCase, Version=0.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d
innermostMethod Elasticsearch.Net.Nest_IHasChildQueryFormatter16.Serialize

[
   {
      "severityLevel":"Error",
      "outerId":"0",
      "message":"Could not load type '' from assembly 'Elasticsearch.Net, Version=7.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d'.",
      "type":"Elasticsearch.Net.UnexpectedElasticsearchClientException",
      "id":"25088443",
      "parsedStack":[
         {
            "assembly":"Elasticsearch.Net, Version=7.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d",
            "method":"Elasticsearch.Net.Transport`1+<RequestAsync>d__15`1.MoveNext",
            "level":0,
            "line":0
         },
         {
            "assembly":"System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e",
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            "level":1,
            "line":0
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         {
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            "level":4,
            "line":0
         },
         {
            "assembly":"Nest, Version=7.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d",
            "method":"Nest.ElasticClient+<SearchAsync>d__266`1.MoveNext",
            "level":5,
            "line":0
         },
         {
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            "method":"System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1+ConfiguredTaskAwaiter.GetResult",
            "level":9,
            "line":0
         },
         {
            "assembly":"Woolworths.Search.Application, Version=1.0.1577.58255, Culture=neutral, PublicKeyToken=null",
            "method":"Woolworths.Search.Application.Executors.WooliesX.WooliesXProductExecutorBase`5+<DoSearchAsync>d__15.MoveNext",
            "level":10,
            "line":256,
            "fileName":"/agent/_work/3/s/src/Search/Woolworths.Search.Application/Executors/WooliesX/WooliesXProductExecutorBase.cs"
         },
         {
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         {
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            "method":"System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1+ConfiguredTaskAwaiter.GetResult",
            "level":14,
            "line":0
         },
         {
            "assembly":"Woolworths.Search.Application, Version=1.0.1577.58255, Culture=neutral, PublicKeyToken=null",
            "method":"Woolworths.Search.Application.Executors.WooliesX.WooliesXProductExecutorBase`5+<DoExecuteAsync>d__10.MoveNext",
            "level":15,
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         {
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            "level":17,
            "line":0
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         {
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            "level":18,
            "line":0
         },
         {
            "assembly":"Woolworths.Search.Application, Version=1.0.1577.58255, Culture=neutral, PublicKeyToken=null",
            "method":"Woolworths.Search.Application.Executors.WooliesX.WooliesXCachedProductV2ExecutorBase`5+<DoExecuteAsync>d__5.MoveNext",
            "level":19,
            "line":0
         },
         {
            "assembly":"System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e",
            "method":"System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw",
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            "line":0
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         {
            "assembly":"System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e",
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            "level":21,
            "line":0
         },
         {
            "assembly":"System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e",
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            "level":22,
            "line":0
         },
         {
            "assembly":"Woolworths.Search.Application, Version=1.0.1577.58255, Culture=neutral, PublicKeyToken=null",
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            "level":26,
            "line":0
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         {
            "assembly":"Woolworths.Search.Application, Version=1.0.1577.58255, Culture=neutral, PublicKeyToken=null",
            "method":"Woolworths.Search.Application.Executors.SearchExecutorBase`2+<ExecuteAsync>d__6.MoveNext",
            "level":27,
            "line":0
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         {
            "assembly":"System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e",
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         {
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            "level":29,
            "line":0
         },
         {
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            "method":"System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification",
            "level":30,
            "line":0
         },
         {
            "assembly":"Woolworths.Search.Application, Version=1.0.1577.58255, Culture=neutral, PublicKeyToken=null",
            "method":"Woolworths.Search.Application.Executors.ElasticSearchExecutor`2+<ExecuteAsync>d__2.MoveNext",
            "level":31,
            "line":0
         }
      ]
   },
   {
      "severityLevel":"Error",
      "outerId":"25088443",
      "message":"Could not load type '' from assembly 'Elasticsearch.Net, Version=7.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d'.",
      "type":"System.TypeLoadException",
      "id":"41968012",
      "parsedStack":[
         {
            "assembly":"Elasticsearch.Net.DynamicObjectResolverAllowPrivateFalseExcludeNullTrueNameMutateCamelCase, Version=0.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d",
            "method":"Elasticsearch.Net.Nest_IHasChildQueryFormatter16.Serialize",
            "level":0,
            "line":0
         },
         {
            "assembly":"Elasticsearch.Net.DynamicObjectResolverAllowPrivateFalseExcludeNullTrueNameMutateCamelCase, Version=0.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d",
            "method":"Elasticsearch.Net.Nest_IQueryContainerFormatter4.Serialize",
            "level":1,
            "line":0
         },
         {
            "assembly":"Nest, Version=7.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d",
            "method":"Nest.QueryContainerCollectionFormatter.Serialize",
            "level":2,
            "line":0
         },
         {
            "assembly":"Elasticsearch.Net.DynamicObjectResolverAllowPrivateFalseExcludeNullTrueNameMutateCamelCase, Version=0.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d",
            "method":"Elasticsearch.Net.Nest_IBoolQueryFormatter5.Serialize",
            "level":3,
            "line":0
         },
         {
            "assembly":"Elasticsearch.Net.DynamicObjectResolverAllowPrivateFalseExcludeNullTrueNameMutateCamelCase, Version=0.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d",
            "method":"Elasticsearch.Net.Nest_IQueryContainerFormatter4.Serialize",
            "level":4,
            "line":0
         },
         {
            "assembly":"Elasticsearch.Net.DynamicObjectResolverAllowPrivateFalseExcludeNullTrueNameMutateCamelCase, Version=0.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d",
            "method":"Elasticsearch.Net.Nest_IBoostingQueryFormatter14.Serialize",
            "level":5,
            "line":0
         },
         {
            "assembly":"Elasticsearch.Net.DynamicObjectResolverAllowPrivateFalseExcludeNullTrueNameMutateCamelCase, Version=0.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d",
            "method":"Elasticsearch.Net.Nest_IQueryContainerFormatter4.Serialize",
            "level":6,
            "line":0
         },
         {
            "assembly":"Elasticsearch.Net.DynamicObjectResolverAllowPrivateFalseExcludeNullTrueNameMutateCamelCase, Version=0.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d",
            "method":"Elasticsearch.Net.Nest_ISearchRequestFormatter1.Serialize",
            "level":7,
            "line":0
         },
         {
            "assembly":"Elasticsearch.Net, Version=7.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d",
            "method":"Elasticsearch.Net.Utf8Json.JsonSerializer+<SerializeAsync>d__11`1.MoveNext",
            "level":8,
            "line":0
         },
         {
            "assembly":"System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e",
            "method":"System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw",
            "level":9,
            "line":0
         },
         {
            "assembly":"System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e",
            "method":"System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess",
            "level":10,
            "line":0
         },
         {
            "assembly":"System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e",
            "method":"System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification",
            "level":11,
            "line":0
         },
         {
            "assembly":"Elasticsearch.Net, Version=7.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d",
            "method":"Elasticsearch.Net.SerializableData`1+<WriteAsync>d__4.MoveNext",
            "level":12,
            "line":0
         },
         {
            "assembly":"System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e",
            "method":"System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw",
            "level":13,
            "line":0
         },
         {
            "assembly":"System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e",
            "method":"System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess",
            "level":14,
            "line":0
         },
         {
            "assembly":"System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e",
            "method":"System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification",
            "level":15,
            "line":0
         },
         {
            "assembly":"Elasticsearch.Net, Version=7.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d",
            "method":"Elasticsearch.Net.HttpConnection+<SetContentAsync>d__25.MoveNext",
            "level":16,
            "line":0
         },
         {
            "assembly":"System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e",
            "method":"System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw",
            "level":17,
            "line":0
         },
         {
            "assembly":"System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e",
            "method":"System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess",
            "level":18,
            "line":0
         },
         {
            "assembly":"System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e",
            "method":"System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification",
            "level":19,
            "line":0
         },
         {
            "assembly":"Elasticsearch.Net, Version=7.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d",
            "method":"Elasticsearch.Net.HttpConnection+<RequestAsync>d__15`1.MoveNext",
            "level":20,
            "line":0
         },
         {
            "assembly":"System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e",
            "method":"System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw",
            "level":21,
            "line":0
         },
         {
            "assembly":"System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e",
            "method":"System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess",
            "level":22,
            "line":0
         },
         {
            "assembly":"System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e",
            "method":"System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification",
            "level":23,
            "line":0
         },
         {
            "assembly":"Elasticsearch.Net, Version=7.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d",
            "method":"Elasticsearch.Net.RequestPipeline+<CallElasticsearchAsync>d__67`1.MoveNext",
            "level":24,
            "line":0
         },
         {
            "assembly":"System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e",
            "method":"System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw",
            "level":25,
            "line":0
         },
         {
            "assembly":"System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e",
            "method":"System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess",
            "level":26,
            "line":0
         },
         {
            "assembly":"System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e",
            "method":"System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification",
            "level":27,
            "line":0
         },
         {
            "assembly":"Elasticsearch.Net, Version=7.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d",
            "method":"Elasticsearch.Net.Transport`1+<RequestAsync>d__15`1.MoveNext",
            "level":28,
            "line":0
         }
      ]
   }
]

ExceptionDetail.AuditTrail.0.Exception.StackTrace
at Elasticsearch.Net.Nest_IHasChildQueryFormatter16.Serialize(JsonWriter&, IHasChildQuery, IJsonFormatterResolver)
at Elasticsearch.Net.Nest_IQueryContainerFormatter4.Serialize(JsonWriter&, IQueryContainer, IJsonFormatterResolver)
at Nest.QueryContainerCollectionFormatter.Serialize(JsonWriter& writer, IEnumerable1 value, IJsonFormatterResolver formatterResolver) at Elasticsearch.Net.Nest_IBoolQueryFormatter5.Serialize(JsonWriter&, IBoolQuery, IJsonFormatterResolver) at Elasticsearch.Net.Nest_IQueryContainerFormatter4.Serialize(JsonWriter&, IQueryContainer, IJsonFormatterResolver) at Elasticsearch.Net.Nest_IBoostingQueryFormatter14.Serialize(JsonWriter&, IBoostingQuery, IJsonFormatterResolver) at Elasticsearch.Net.Nest_IQueryContainerFormatter4.Serialize(JsonWriter&, IQueryContainer, IJsonFormatterResolver) at Elasticsearch.Net.Nest_ISearchRequestFormatter1.Serialize(JsonWriter&, ISearchRequest, IJsonFormatterResolver) at Elasticsearch.Net.Utf8Json.JsonSerializer.SerializeAsync[T](Stream stream, T value, IJsonFormatterResolver resolver) at Elasticsearch.Net.SerializableData1.WriteAsync(Stream writableStream, IConnectionConfigurationValues settings, CancellationToken cancellationToken)
at Elasticsearch.Net.HttpConnection.SetContentAsync(HttpRequestMessage message, RequestData requestData, CancellationToken cancellationToken)
at Elasticsearch.Net.HttpConnection.RequestAsync[TResponse](RequestData requestData, CancellationToken cancellationToken)
at Elasticsearch.Net.RequestPipeline.CallElasticsearchAsync[TResponse](RequestData requestData, CancellationToken cancellationToken)
at Elasticsearch.Net.Transport`1.RequestAsync[TResponse](HttpMethod method, String path, CancellationToken cancellationToken, PostData data, IRequestParameters requestParameters)

ExceptionDetail.InnerException.Message Could not load type '' from assembly 'Elasticsearch.Net, Version=7.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d'.
ExceptionDetail.InnerException.Source Elasticsearch.Net.DynamicObjectResolverAllowPrivateFalseExcludeNullTrueNameMutateCamelCase
ExceptionDetail.InnerException.TargetSite Void Serialize(Elasticsearch.Net.Utf8Json.JsonWriter ByRef, Nest.IHasChildQuery, Elasticsearch.Net.Utf8Json.IJsonFormatterResolver)
ExceptionDetail.InnerException.Type System.TypeLoadException
ExceptionDetail.Message Could not load type '' from assembly 'Elasticsearch.Net, Version=7.0.0.0, Culture=neutral, PublicKeyToken=96c599bbe3e70f5d'.
ExceptionDetail.SeenExceptions.Count 0
ExceptionDetail.Source Elasticsearch.Net
ExceptionDetail.TargetSite Void MoveNext()
ExceptionDetail.Type Elasticsearch.Net.UnexpectedElasticsearchClientException

The only workaround I have in place at the moment is to get an warning from Azure Logs as soon as one System.TypeLoadException happens and I kill that pod.

These are the packages I've in my project that share an instance of Nest.ElasticClient when I run a request and try building an ES query:

<PackageReference Include="Elastic.Clients.Elasticsearch" Version="8.14.1" />
<PackageReference Include="NEST.JsonNetSerializer" Version="7.17.5" />

[flobernd]

Hi @felipedrumond , what version of the .NET framework are you using?

The Utf8Json package does not seem to work well with newer TFMs and causes these kinds of exceptions.

[felipedrumond]

@flobernd I'm using
<TargetFramework>net8.0</TargetFramework>

[flobernd]

@felipedrumond That confirms my guess that it is the same incompatibility with the Utf8Json dependency as in the other issues.

Is there any chance you could upgrade to the new V8 client?

While NEST continues to be supported until end of this year, we announced not to implement any feature updates.

This particular case is a bit in a grey zone as we technically experience a bug and netstandard builds should work fine with net8. This seems not the case here.

Migrating to a newer version of the dependency would require a significant amount of work (as we have to as well adjust tests, build system, etc. etc. to add a dedicated net8 TFM to NEST) so that we currently consider this a feature aka. "won't fix".

As an alternative you could lower your projects TFM to one of the older, supported, version.

[felipedrumond]

@flobernd thanks!

So this problem would happen when the Nest.ElasticClient is used to connect to Elasticseach in a .net 8/9 project, right?

I though the problem was caused by my code mixing Elasticsearch.Net.SingleNodeConnectionPool and Elasticsearch.Net.ApiKeyAuthenticationCredentials while creating Nest.ElasticClient to connect to Elasticsearch.

[flobernd]

@felipedrumond It's kinda hard to track down, but something seems to go wrong with IL code generation in combination with Utf8Json and newer .NET frameworks. I don't think it's your code that's causing this.