Symptom
When you stress test an HTTPS API, response time (RT) gradually increases while transactions per second (TPS) and success rate drop to zero or trend toward zero. The sampling log reports the following error:
The following error message appears in the sampling log:
java.net.SocketException: Socket closed
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:589)
at sun.security.ssl.SSLSocketImpl.connect(SSLSocketImpl.java:668)
at org.apache.http.conn.ssl.SSLSocketFactory.connectSocket(SSLSocketFactory.java:542)
at org.apache.http.conn.ssl.SSLSocketFactory.connectSocket(SSLSocketFactory.java:414)
at org.apache.jmeter.protocol.http.sampler.LazySchemeSocketFactory.connectSocket(LazySchemeSocketFactory.java:97)
at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:180)
at org.apache.jmeter.protocol.http.sampler.hc.ManagedClientConnectionImpl.open(ManagedClientConnectionImpl.java:318)
at org.apache.jmeter.protocol.http.sampler.MeasuringConnectionManager$MeasuredConnection.open(MeasuringConnectionManager.java:114)
at org.apache.http.impl.client.DefaultRequestDirector.tryConnect(DefaultRequestDirector.java:610)
at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:445)
at org.apache.http.impl.client.AbstractHttpClient.doExecute(AbstractHttpClient.java:835)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:83)
at org.apache.jmeter.protocol.http.sampler.HTTPHC4Impl.executeRequest(HTTPHC4Impl.java:695)
at org.apache.jmeter.protocol.http.sampler.HTTPHC4Impl.sample(HTTPHC4Impl.java:454)
at org.apache.jmeter.protocol.http.sampler.HTTPSamplerProxy.sample(HTTPSamplerProxy.java:74)
at org.apache.jmeter.protocol.http.sampler.HTTPSamplerBase.sample(HTTPSamplerBase.java:1189)
at org.apache.jmeter.protocol.http.sampler.HTTPSamplerBase.sample(HTTPSamplerBase.java:1178)
at org.apache.jmeter.threads.JMeterThread.executeSamplePackage(JMeterThread.java:498)
at org.apache.jmeter.threads.JMeterThread.processSampler(JMeterThread.java:424)
at org.apache.jmeter.threads.JMeterThread.run(JMeterThread.java:255)
at java.lang.Thread.run(Thread.java:766)
The Timing Waterfall in the sampling log confirms that all time is spent during the connection establishment phase.
Cause
In most cases, this error occurs because no connection timeout period is configured.
Solution
Confirm that KeepAlive is enabled
On the Basic tab of the HTTP request sampler, verify that Use KeepAlive is selected.
Configure the connection timeout
On the Advanced tab of the HTTP request sampler, configure the following parameters:
Set Implementation to HttpClient4.
Set Connect to a value between 10 and 60 seconds as the idle connection timeout period. This prevents the connection from being disconnected due to the failure to receive the Keep-Alive header returned by the stress testing server.
Verify the fix
After you apply the configuration, run a short stress test with reduced concurrency. Check the sampling log to confirm that:
The java.net.SocketException: Socket closed error no longer appears.
The Timing Waterfall no longer shows excessive time in the connection establishment phase.
RT, TPS, and success rate remain stable throughout the test.