Apache Nifi - Unable to communicate to Nifi when trying to view the file content of Generate FlowFile

[#1]

I am new to Apache. I have generated files using Generate Flow File processor but when I try to view the file content it gives me UI error "Unable to communicate to NiFi" I think there is a problem with content file viewer in NiFi.

I am using https and port 8443 and also when I download the file the content in the file appears all okay just that it's not working in the browser!

[#2]

Hello @Runa27, 

Thanks for being part of our community. 

Several reasons could lead on this, but the main two I can think are these: 
1. You do not have the web proxy enabled. Add this setting and test: nifi.web.proxy.host=UIhostname:8443
2. The files are big and the browser is restricting the big response. 

Now, what can help here is to see the nifi-app.log at the moment of the failure, it may give us some clues. 

[#3]

@vafs I have tried the solution 1 but still it's the same problem. Also the file is not big it's just 1 file with 10 bytes.

Here is the last rows of log file:

2026-01-19 21:39:38,488 INFO [main] o.a.n.f.s.StandardVersionedComponentSynchronizer Updating StandardProcessGroup[identifier=cd1c3991-019b-1000-73b3-45a1c5599ab2,name=NiFi Flow] to org.apache.nifi.flow.VersionedExternalFlow@4e7e42c4; there are 10 differences to take into account:
Processor with ID d4f095c5-019b-1000-590d-c16a641f13bc exists in Proposed Flow but not in Currently Loaded Flow
Processor with ID d4e31223-019b-1000-0dc0-bb6a49a42e54 exists in Proposed Flow but not in Currently Loaded Flow
Connection with ID d4f0bced-019b-1000-048e-765fab2ec7e4 exists in Proposed Flow but not in Currently Loaded Flow
Connection with ID d4e4d8ba-019b-1000-5539-da6aefff28bc exists in Proposed Flow but not in Currently Loaded Flow
Processor with ID d043e64b-019b-1000-cd66-0d6bc2e4a711 exists in Proposed Flow but not in Currently Loaded Flow
Connection with ID d0450dbc-019b-1000-c6e8-f9c7be7f7295 exists in Proposed Flow but not in Currently Loaded Flow
Processor with ID d1b881e7-019b-1000-b6b4-d7188d007cbd exists in Proposed Flow but not in Currently Loaded Flow
Processor with ID cfd26ca3-019b-1000-7948-eb8c9ec17195 exists in Proposed Flow but not in Currently Loaded Flow
Processor with ID d4f849e2-019b-1000-a95c-364939018b8a exists in Proposed Flow but not in Currently Loaded Flow
Connection with ID d5014822-019b-1000-8de6-575ee783acff exists in Proposed Flow but not in Currently Loaded Flow
2026-01-19 21:39:38,562 INFO [main] o.a.nifi.groups.StandardProcessGroup ExtractText[id=d4f849e2-019b-1000-a95c-364939018b8a] added to StandardProcessGroup[identifier=cd1c3991-019b-1000-73b3-45a1c5599ab2,name=NiFi Flow]
2026-01-19 21:39:38,592 INFO [main] o.a.n.f.s.StandardVersionedComponentSynchronizer Added ExtractText[id=d4f849e2-019b-1000-a95c-364939018b8a] to StandardProcessGroup[identifier=cd1c3991-019b-1000-73b3-45a1c5599ab2,name=NiFi Flow]
2026-01-19 21:39:38,600 INFO [main] o.a.nifi.groups.StandardProcessGroup LogAttribute[id=d4f095c5-019b-1000-590d-c16a641f13bc] added to StandardProcessGroup[identifier=cd1c3991-019b-1000-73b3-45a1c5599ab2,name=NiFi Flow]
2026-01-19 21:39:38,602 INFO [main] o.a.n.f.s.StandardVersionedComponentSynchronizer Added LogAttribute[id=d4f095c5-019b-1000-590d-c16a641f13bc] to StandardProcessGroup[identifier=cd1c3991-019b-1000-73b3-45a1c5599ab2,name=NiFi Flow]
2026-01-19 21:39:38,610 INFO [main] o.a.nifi.groups.StandardProcessGroup GenerateFlowFile[id=d1b881e7-019b-1000-b6b4-d7188d007cbd] added to StandardProcessGroup[identifier=cd1c3991-019b-1000-73b3-45a1c5599ab2,name=NiFi Flow]
2026-01-19 21:39:38,611 INFO [main] o.a.n.f.s.StandardVersionedComponentSynchronizer Added GenerateFlowFile[id=d1b881e7-019b-1000-b6b4-d7188d007cbd] to StandardProcessGroup[identifier=cd1c3991-019b-1000-73b3-45a1c5599ab2,name=NiFi Flow]
2026-01-19 21:39:38,624 INFO [main] o.a.nifi.groups.StandardProcessGroup PutFile[id=d043e64b-019b-1000-cd66-0d6bc2e4a711] added to StandardProcessGroup[identifier=cd1c3991-019b-1000-73b3-45a1c5599ab2,name=NiFi Flow]
2026-01-19 21:39:38,625 INFO [main] o.a.n.f.s.StandardVersionedComponentSynchronizer Added PutFile[id=d043e64b-019b-1000-cd66-0d6bc2e4a711] to StandardProcessGroup[identifier=cd1c3991-019b-1000-73b3-45a1c5599ab2,name=NiFi Flow]
2026-01-19 21:39:38,640 INFO [main] o.a.nifi.groups.StandardProcessGroup ReplaceText[id=d4e31223-019b-1000-0dc0-bb6a49a42e54] added to StandardProcessGroup[identifier=cd1c3991-019b-1000-73b3-45a1c5599ab2,name=NiFi Flow]
2026-01-19 21:39:38,641 INFO [main] o.a.n.f.s.StandardVersionedComponentSynchronizer Added ReplaceText[id=d4e31223-019b-1000-0dc0-bb6a49a42e54] to StandardProcessGroup[identifier=cd1c3991-019b-1000-73b3-45a1c5599ab2,name=NiFi Flow]
2026-01-19 21:39:38,647 INFO [main] o.a.nifi.groups.StandardProcessGroup GetFile[id=cfd26ca3-019b-1000-7948-eb8c9ec17195] added to StandardProcessGroup[identifier=cd1c3991-019b-1000-73b3-45a1c5599ab2,name=NiFi Flow]
2026-01-19 21:39:38,648 INFO [main] o.a.n.f.s.StandardVersionedComponentSynchronizer Added GetFile[id=cfd26ca3-019b-1000-7948-eb8c9ec17195] to StandardProcessGroup[identifier=cd1c3991-019b-1000-73b3-45a1c5599ab2,name=NiFi Flow]
2026-01-19 21:39:38,676 INFO [main] o.a.n.f.s.StandardVersionedComponentSynchronizer Added Connection[ID=d4f0bced-019b-1000-048e-765fab2ec7e4, Source ID=d4e31223-019b-1000-0dc0-bb6a49a42e54, Dest ID=d4f849e2-019b-1000-a95c-364939018b8a] to StandardProcessGroup[identifier=cd1c3991-019b-1000-73b3-45a1c5599ab2,name=NiFi Flow]
2026-01-19 21:39:38,678 INFO [main] o.a.n.f.s.StandardVersionedComponentSynchronizer Added Connection[ID=d4e4d8ba-019b-1000-5539-da6aefff28bc, Source ID=d1b881e7-019b-1000-b6b4-d7188d007cbd, Dest ID=d4e31223-019b-1000-0dc0-bb6a49a42e54] to StandardProcessGroup[identifier=cd1c3991-019b-1000-73b3-45a1c5599ab2,name=NiFi Flow]
2026-01-19 21:39:38,679 INFO [main] o.a.n.f.s.StandardVersionedComponentSynchronizer Added Connection[ID=d5014822-019b-1000-8de6-575ee783acff, Source ID=d4f849e2-019b-1000-a95c-364939018b8a, Dest ID=d4f095c5-019b-1000-590d-c16a641f13bc] to StandardProcessGroup[identifier=cd1c3991-019b-1000-73b3-45a1c5599ab2,name=NiFi Flow]
2026-01-19 21:39:38,680 INFO [main] o.a.n.f.s.StandardVersionedComponentSynchronizer Added Connection[ID=d0450dbc-019b-1000-c6e8-f9c7be7f7295, Source ID=cfd26ca3-019b-1000-7948-eb8c9ec17195, Dest ID=d043e64b-019b-1000-cd66-0d6bc2e4a711] to StandardProcessGroup[identifier=cd1c3991-019b-1000-73b3-45a1c5599ab2,name=NiFi Flow]
2026-01-19 21:39:38,710 INFO [main] o.a.n.c.s.VersionedFlowSynchronizer After synchronizing flow, restarting 0 components
2026-01-19 21:39:38,710 INFO [main] o.a.n.c.s.AffectedComponentSet Starting the following components: AffectedComponentSet[inputPorts=[], outputPorts=[], remoteInputPorts=[], remoteOutputPorts=[], processors=[], parameterProviders=[], flowRegistryClients=[], controllerServices=[], reportingTasks=[], flowAnalysisRules=[], statelessProcessGroups=[]]
2026-01-19 21:39:38,711 INFO [main] o.a.n.c.s.VersionedFlowSynchronizer Successfully synchronized dataflow with the proposed flow in 490 millis
2026-01-19 21:39:38,712 INFO [main] o.apache.nifi.controller.FlowController Successfully synchronized controller with proposed flow. Flow contains the following number of components: {Processors=6, Controller Services=0, Reporting Tasks=0, Flow Analysis Rules=0, Process Groups=0, Remote Process Groups=0, Parameter Providers=0, Flow Registry Clients=0, Local Input Ports=0, Local Output Ports=0, Public Input Ports=0, Public Output Ports=0}
2026-01-19 21:39:38,718 INFO [main] o.a.n.c.r.WriteAheadFlowFileRepository Successfully restored 1 FlowFiles and 0 Swap Files
2026-01-19 21:39:38,893 INFO [main] o.apache.nifi.controller.FlowController Scheduled Flow Registry synchronization every 30 min
2026-01-19 21:39:39,007 INFO [main] o.apache.nifi.controller.FlowController Performed initial validation of all components in 19 milliseconds
2026-01-19 21:39:39,007 INFO [main] o.apache.nifi.controller.FlowController Starting 0 Stateless Process Groups
2026-01-19 21:39:39,008 INFO [main] o.apache.nifi.controller.FlowController Starting 0 processors/ports/funnels
2026-01-19 21:39:39,008 INFO [main] o.apache.nifi.controller.FlowController Started 0 Remote Group Ports transmitting
2026-01-19 21:39:39,008 INFO [main] o.a.n.w.c.ApplicationStartupContextListener Flow Controller started successfully.
2026-01-19 21:39:40,717 INFO [main] o.e.j.ee11.servlet.ServletContextHandler Started oeje11w.WebAppContext@7845b21a{nifi-api,/nifi-api,b=file:///C:/nifi-2.7.2-bin/nifi-2.7.2/work/jetty/nifi-web-api-2.7.2.war/webapp/,a=AVAILABLE,h=oeje11s.SessionHandler@1a0d313{STARTED}}{.\work\nar\extensions\nifi-server-nar-2.7.2.nar-unpacked\NAR-INF\bundled-dependencies\nifi-web-api-2.7.2.war}
2026-01-19 21:39:41,246 INFO [main] o.e.j.s.handler.ContextHandler._nifi No Spring WebApplicationInitializer types detected on classpath
2026-01-19 21:39:41,305 INFO [main] o.e.jetty.server.handler.ContextHandler Started oeje11w.WebAppContext@123fb86b{/nifi,/nifi,b=file:///C:/nifi-2.7.2-bin/nifi-2.7.2/work/jetty/nifi-ui-2.7.2.war/webapp/,a=AVAILABLE,h=oeje11s.SessionHandler@7d053139{STARTED}}{.\work\nar\extensions\nifi-server-nar-2.7.2.nar-unpacked\NAR-INF\bundled-dependencies\nifi-ui-2.7.2.war}
2026-01-19 21:39:41,310 INFO [main] o.e.j.ee11.servlet.ServletContextHandler Started oeje11w.WebAppContext@123fb86b{/nifi,/nifi,b=file:///C:/nifi-2.7.2-bin/nifi-2.7.2/work/jetty/nifi-ui-2.7.2.war/webapp/,a=AVAILABLE,h=oeje11s.SessionHandler@7d053139{STARTED}}{.\work\nar\extensions\nifi-server-nar-2.7.2.nar-unpacked\NAR-INF\bundled-dependencies\nifi-ui-2.7.2.war}
2026-01-19 21:39:41,347 INFO [main] o.eclipse.jetty.server.AbstractConnector Started oejs.ServerConnector@4251661c{SSL, (ssl, alpn, h2, http/1.1)}{localhost:٨٤٤٣}
2026-01-19 21:39:41,348 INFO [main] org.eclipse.jetty.server.Server Started oejs.Server@37a0ec3c{STARTING}[12.1.5,sto=٠] @33077ms
2026-01-19 21:39:41,351 INFO [main] org.apache.nifi.web.server.JettyServer Started Server on https://localhost:8443/nifi
2026-01-19 21:39:41,374 INFO [main] o.a.n.runtime.StandardManagementServer Started Management Server on http://127.0.0.1:9990
2026-01-19 21:39:41,376 INFO [main] org.apache.nifi.runtime.Application Started Application in 41.014 seconds (41014935800 ns)
2026-01-19 21:39:58,724 INFO [Checkpoint FlowFile Repository] o.a.n.c.r.WriteAheadFlowFileRepository Successfully checkpointed FlowFile Repository with 1 records in 0 milliseconds
2026-01-19 21:40:01,600 INFO [NiFi Web Server-144] o.a.s.c.u.s.b.BouncyCastleSecurityProviderRegistrar getOrCreateProvider(BC) created instance of org.bouncycastle.jce.provider.BouncyCastleProvider
2026-01-19 21:40:10,074 INFO [NiFi Web Server-113] o.a.n.c.queue.AbstractFlowFileQueue Canceling ListFlowFile Request with ID d78ea333-019b-1000-15f9-41102ef45dce
2026-01-19 21:40:18,739 INFO [Checkpoint FlowFile Repository] o.a.n.c.r.WriteAheadFlowFileRepository Successfully checkpointed FlowFile Repository with 1 records in 0 milliseconds
2026-01-19 21:40:31,730 INFO [Cleanup Archive for default] o.a.n.c.repository.FileSystemRepository Successfully deleted 0 files (٠ bytes) from archive
2026-01-19 21:40:31,731 INFO [Cleanup Archive for default] o.a.n.c.repository.FileSystemRepository Archive cleanup completed for container default; will now allow writing to this container. Bytes used = ١٢٣٫٣٢ GB, bytes free = ١١٥٫٠٤ GB, capacity = ٢٣٨٫٣٦ GB
2026-01-19 21:40:38,743 INFO [Checkpoint FlowFile Repository] o.a.n.c.r.WriteAheadFlowFileRepository Successfully checkpointed FlowFile Repository with 1 records in 0 milliseconds
2026-01-19 21:40:58,757 INFO [Checkpoint FlowFile Repository] o.a.n.c.r.WriteAheadFlowFileRepository Successfully checkpointed FlowFile Repository with 1 records in 0 milliseconds
2026-01-19 21:41:18,762 INFO [Checkpoint FlowFile Repository] o.a.n.c.r.WriteAheadFlowFileRepository Successfully checkpointed FlowFile Repository with 1 records in 0 milliseconds
2026-01-19 21:41:22,925 INFO [Write-Ahead Local State Provider Maintenance] o.a.n.wali.SequentialAccessWriteAheadLog Checkpointed Write-Ahead Log with 3 Records and 0 Swap Files in 18 milliseconds (Stop-the-world time = 7 milliseconds), max Transaction ID 47
2026-01-19 21:41:31,861 INFO [Cleanup Archive for default] o.a.n.c.repository.FileSystemRepository Successfully deleted 0 files (٠ bytes) from archive
2026-01-19 21:41:31,862 INFO [Cleanup Archive for default] o.a.n.c.repository.FileSystemRepository Archive cleanup completed for container default; will now allow writing to this container. Bytes used = ١٢٣٫٣٢ GB, bytes free = ١١٥٫٠٤ GB, capacity = ٢٣٨٫٣٦ GB
2026-01-19 21:41:38,773 INFO [Checkpoint FlowFile Repository] o.a.n.c.r.WriteAheadFlowFileRepository Successfully checkpointed FlowFile Repository with 1 records in 0 milliseconds
2026-01-19 21:41:58,779 INFO [Checkpoint FlowFile Repository] o.a.n.c.r.WriteAheadFlowFileRepository Successfully checkpointed FlowFile Repository with 1 records in 0 milliseconds
2026-01-19 21:42:18,787 INFO [Checkpoint FlowFile Repository] o.a.n.c.r.WriteAheadFlowFileRepository Successfully checkpointed FlowFile Repository with 1 records in 0 milliseconds
2026-01-19 21:42:31,955 INFO [Cleanup Archive for default] o.a.n.c.repository.FileSystemRepository Successfully deleted 0 files (٠ bytes) from archive
2026-01-19 21:42:31,956 INFO [Cleanup Archive for default] o.a.n.c.repository.FileSystemRepository Archive cleanup completed for container default; will now allow writing to this container. Bytes used = ١٢٣٫٣٣ GB, bytes free = ١١٥٫٠٣ GB, capacity = ٢٣٨٫٣٦ GB
2026-01-19 21:42:38,794 INFO [Checkpoint FlowFile Repository] o.a.n.c.r.WriteAheadFlowFileRepository Successfully checkpointed FlowFile Repository with 1 records in 0 milliseconds

[#4]

@Runa27 

Before being able to properly help we need you to share your exact Apache NiFi version details.  This allows us to see if your are experiencing a known issue in your specific version. 
 
Also you'll want to tail the nifi-user.log and nifi-app.log when you make the request to view the content.  Then share the output from both those files covering the time of that request (please include time when you performed request via NiFi UI).

Also share a bit more about your NiFi setup.  What method of user authentication and user authorization are you using?

Please help our community grow. If you found any of the suggestions/solutions provided helped you with solving your issue or answering your question, please take a moment to login and click "Accept as Solution" on one or more of them that helped.

Thank you,
Matt

[#5]

@MattWho 

My apache version is 2.7.2 

I’m using HTTPS with NiFi’s Single User authentication and file-based authorization. I think it's called standalone (I'm still beginner)

The time I performed the request was at 21:58

User-log:

2026-01-21 21:03:30,196 INFO [main] o.a.n.a.single.user.SingleUserAuthorizer Initializing Authorizer
2026-01-21 21:03:30,217 INFO [main] o.a.n.a.single.user.SingleUserAuthorizer Configuring Authorizer
2026-01-21 21:03:41,567 INFO [main] o.a.n.w.s.c.KeyPairGeneratorConfiguration Configured Key Pair Algorithm [Ed25519] for JSON Web Signatures

app-log:

 (٠ bytes) from archive
2026-01-21 21:56:41,684 INFO [Cleanup Archive for default] o.a.n.c.repository.FileSystemRepository Archive cleanup completed for container default; will now allow writing to this container. Bytes used = ١١٩٫٧٧ GB, bytes free = ١١٨٫٥٩ GB, capacity = ٢٣٨٫٣٦ GB
2026-01-21 21:56:46,060 INFO [Checkpoint FlowFile Repository] o.a.n.c.r.WriteAheadFlowFileRepository Successfully checkpointed FlowFile Repository with 3 records in 0 milliseconds
2026-01-21 21:57:06,063 INFO [Checkpoint FlowFile Repository] o.a.n.c.r.WriteAheadFlowFileRepository Successfully checkpointed FlowFile Repository with 3 records in 0 milliseconds
2026-01-21 21:57:26,070 INFO [Checkpoint FlowFile Repository] o.a.n.c.r.WriteAheadFlowFileRepository Successfully checkpointed FlowFile Repository with 3 records in 0 milliseconds
2026-01-21 21:57:41,825 INFO [Cleanup Archive for default] o.a.n.c.repository.FileSystemRepository Successfully deleted 0 files (٠ bytes) from archive
2026-01-21 21:57:41,826 INFO [Cleanup Archive for default] o.a.n.c.repository.FileSystemRepository Archive cleanup completed for container default; will now allow writing to this container. Bytes used = ١١٩٫٨١ GB, bytes free = ١١٨٫٥٥ GB, capacity = ٢٣٨٫٣٦ GB
2026-01-21 21:57:46,080 INFO [Checkpoint FlowFile Repository] o.a.n.c.r.WriteAheadFlowFileRepository Successfully checkpointed FlowFile Repository with 3 records in 0 milliseconds
2026-01-21 21:57:59,744 INFO [NiFi Web Server-43] o.a.n.c.s.StandardProcessScheduler Starting GetFile[id=df248648-019b-1000-d364-3157623c6fa5]
2026-01-21 21:57:59,744 INFO [NiFi Web Server-43] o.a.n.controller.StandardProcessorNode Desired State for GetFile[id=df248648-019b-1000-d364-3157623c6fa5] now set to RUNNING
2026-01-21 21:57:59,750 INFO [Timer-Driven Process Thread-10] o.a.n.c.s.TimerDrivenSchedulingAgent Scheduled GetFile[id=df248648-019b-1000-d364-3157623c6fa5] to run with 1 threads
2026-01-21 21:57:59,769 INFO [Timer-Driven Process Thread-1] o.a.n.p.store.WriteAheadStorePartition Successfully rolled over Event Writer for Provenance Event Store Partition[directory=.\provenance_repository] due to MAX_TIME_REACHED. Event File was ١٨٫٢٦ KB and contained 9 events.
2026-01-21 21:58:00,142 INFO [Flow Service Tasks Thread-2] o.a.nifi.controller.StandardFlowService Saved flow controller org.apache.nifi.controller.FlowController@521c794a // Another save pending = false
2026-01-21 21:58:06,090 INFO [Checkpoint FlowFile Repository] o.a.n.wali.SequentialAccessWriteAheadLog Checkpointed Write-Ahead Log with 4 Records and 0 Swap Files in 5 milliseconds (Stop-the-world time = 2 milliseconds), max Transaction ID 20115
2026-01-21 21:58:06,090 INFO [Checkpoint FlowFile Repository] o.a.n.c.r.WriteAheadFlowFileRepository Successfully checkpointed FlowFile Repository with 4 records in 6 milliseconds
2026-01-21 21:58:18,911 INFO [NiFi Web Server-127] o.a.n.c.s.StandardProcessScheduler Stopping GetFile[id=df248648-019b-1000-d364-3157623c6fa5]
2026-01-21 21:58:18,911 INFO [NiFi Web Server-127] o.a.n.controller.StandardProcessorNode Desired State for GetFile[id=df248648-019b-1000-d364-3157623c6fa5] now set to STOPPED
2026-01-21 21:58:18,912 INFO [Timer-Driven Process Thread-8] o.a.n.c.s.TimerDrivenSchedulingAgent Stopped scheduling GetFile[id=df248648-019b-1000-d364-3157623c6fa5] to run
2026-01-21 21:58:19,027 INFO [Timer-Driven Process Thread-8] o.a.n.controller.StandardProcessorNode GetFile[id=df248648-019b-1000-d364-3157623c6fa5] has completely stopped. Completing any associated Futures.
2026-01-21 21:58:19,450 INFO [Flow Service Tasks Thread-1] o.a.nifi.controller.StandardFlowService Saved flow controller org.apache.nifi.controller.FlowController@521c794a // Another save pending = false
2026-01-21 21:58:24,878 INFO [NiFi Web Server-44] o.a.n.c.queue.AbstractFlowFileQueue Canceling ListFlowFile Request with ID e1ec0fce-019b-1000-58ba-5a4490a069da
2026-01-21 21:58:26,094 INFO [Checkpoint FlowFile Repository] o.a.n.c.r.WriteAheadFlowFileRepository Successfully checkpointed FlowFile Repository with 4 records in 0 milliseconds