David Handermann created NIFI-9448:
--------------------------------------

             Summary: Potential IllegalStateException when S2S HTTP Client 
Shutdown
                 Key: NIFI-9448
                 URL: https://issues.apache.org/jira/browse/NIFI-9448
             Project: Apache NiFi
          Issue Type: Bug
          Components: Core Framework
    Affects Versions: 1.15.0
            Reporter: David Handermann
            Assignee: David Handermann


NiFi Site-to-Site communication over HTTP relies on {{SiteToSiteRestApiClient}} 
to handle requests and responses using the Apache HttpComponents library. The 
HttpComponents library maintains a connection pool for processing HTTP 
transactions.

In the course of sending or receiving files, NiFi starts a background thread to 
make periodic requests to the remote NiFi system in order to extend the current 
transaction. The {{SiteToSiteRestApiClient}} stops the background thread after 
completing a transaction. In some cases, the request to extend the transaction 
can occur after the HttpComponents connection pool is shutdown, resulting in an 
{{{}IllegalStateException{}}}. The background thread treats all exceptions as 
failure conditions and then attempts to close the S2S HTTP client itself. This 
causes subsequent retry requests using the same {{SiteToSiteRestApiClient}} to 
fail with the same {{IllegalStateException}} indicating that the connection 
pool is shutdown.

The behavior of the extend transaction command should be changed to avoid 
closing the S2S HTTP client when encountering an {{IllegalStateException}}. 
This approach will support the potential for subsequent retries to work or fail 
based on existing timeout configuration settings.

The following log messages provide a stack trace of the 
{{IllegalStateException}} in the extend transaction command and subsequent 
exception in the Remote Process Group Port connection.

{noformat}
WARN org.apache.nifi.remote.util.SiteToSiteRestApiClient: Failed to extend 
transaction ttl
java.lang.IllegalStateException: Connection pool shut down
        at org.apache.http.util.Asserts.check(Asserts.java:34)
        at 
org.apache.http.pool.AbstractConnPool.lease(AbstractConnPool.java:191)
        at 
org.apache.http.impl.conn.PoolingHttpClientConnectionManager.requestConnection(PoolingHttpClientConnectionManager.java:267)
        at 
org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:176)
        at 
org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:185)
        at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:89)
        at 
org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:111)
        at 
org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:185)
        at 
org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:83)
        at 
org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:108)
        at 
org.apache.nifi.remote.util.SiteToSiteRestApiClient.extendTransaction(SiteToSiteRestApiClient.java:1028)
        at 
org.apache.nifi.remote.util.SiteToSiteRestApiClient.lambda$startExtendingTtl$0(SiteToSiteRestApiClient.java:990)
        at 
java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
        at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
        at 
java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180)
        at 
java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294)
        at 
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at 
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)
2021-11-10 08:17:10,352 INFO org.apache.http.impl.execchain.RetryExec: I/O 
exception (org.apache.http.NoHttpResponseException) caught when processing 
request: The target server failed to respond
INFO org.apache.http.impl.execchain.RetryExec: Retrying request
ERROR org.apache.nifi.remote.StandardRemoteGroupPort: 
RemoteGroupPort[name=REMOTE_PORT,targets=URL] failed to communicate with remote 
NiFi instance due to java.lang.IllegalStateException: Connection pool shut down
{noformat}



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