Sonarqube background analysis fails, reports smells plugin does not exist - jenkins

Question

I have a brand new sonarqube installation (6.7.1.35068) which is being invoked from a brand-new jenkins server (2.102) using the maven goal. Both are running as services on ec2-linux which is fully patched.
At first it worked.
Then, it sonar began reporting:
java.lang.IllegalArgumentException: Plugin [smells] does not exist
and refusing to run the background analysis, although the jenkins build reports success.
I can run the jenkins job twice in a row and get a success and a failure without changing anything in the servers or the code. And then three failures in a row, then four successes in a row.
The plugin does indeed exist, and the sonar server show it is loaded in its configuration reporting.
I have looked at file permissions on the machine, and everything seems to be owned by the right user with the right permissions.
Has anyone seen this behavior? Any ideas about what other troubleshooting I could do?
Many thanks for any help.
EDIT: Here is the content of sonar.log at startup.
--> Wrapper Started as Daemon
Launching a JVM...
Wrapper (Version 3.2.3) http://wrapper.tanukisoftware.org
Copyright 1999-2006 Tanuki Software, Inc. All Rights Reserved.
2018.01.22 13:48:02 INFO app[][o.s.a.AppFileSystem] Cleaning or creating temp directory /opt/sonar/temp
2018.01.22 13:48:02 INFO app[][o.s.a.es.EsSettings] Elasticsearch listening on /127.0.0.1:9001
2018.01.22 13:48:02 INFO app[][o.s.a.p.ProcessLauncherImpl] Launch process[[key='es', ipcIndex=1, logFilenamePrefix=es]] from [/opt/sonar/elasticsearch]: /opt/sonar/elasticsearch/bin/elasticsearch -Epath.conf=/opt/sonar/temp/conf/es
2018.01.22 13:48:03 INFO app[][o.s.a.SchedulerImpl] Waiting for Elasticsearch to be up and running
2018.01.22 13:48:03 INFO app[][o.e.p.PluginsService] no modules loaded
2018.01.22 13:48:03 INFO app[][o.e.p.PluginsService] loaded plugin [org.elasticsearch.transport.Netty4Plugin]
2018.01.22 13:48:12 INFO app[][o.s.a.SchedulerImpl] Process[es] is up
2018.01.22 13:48:12 INFO app[][o.s.a.p.ProcessLauncherImpl] Launch process[[key='web', ipcIndex=2, logFilenamePrefix=web]] from [/opt/sonar]: /usr/java/jdk1.8.0_121/jre/bin/java -Djava.awt.headless=true -Dfile.encoding=UTF-8 -Djava.io.tmpdir=/opt/sonar/temp -Xmx512m -Xms128m -XX:+HeapDumpOnOutOfMemoryError -cp ./lib/common/*:./lib/server/*:/opt/sonar/lib/jdbc/postgresql/postgresql-42.1.4.jar org.sonar.server.app.WebServer /opt/sonar/temp/sq-process7588018711976818336properties
2018.01.22 13:48:28 INFO app[][o.s.a.SchedulerImpl] Process[web] is up
2018.01.22 13:48:28 INFO app[][o.s.a.p.ProcessLauncherImpl] Launch process[[key='ce', ipcIndex=3, logFilenamePrefix=ce]] from [/opt/sonar]: /usr/java/jdk1.8.0_121/jre/bin/java -Djava.awt.headless=true -Dfile.encoding=UTF-8 -Djava.io.tmpdir=/opt/sonar/temp -Xmx512m -Xms128m -XX:+HeapDumpOnOutOfMemoryError -cp ./lib/common/*:./lib/server/*:./lib/ce/*:/opt/sonar/lib/jdbc/postgresql/postgresql-42.1.4.jar org.sonar.ce.app.CeServer /opt/sonar/temp/sq-process7608302589622094268properties
2018.01.22 13:48:37 INFO app[][o.s.a.SchedulerImpl] Process[ce] is up
2018.01.22 13:48:37 INFO app[][o.s.a.SchedulerImpl] SonarQube is up
And that "no modules loaded" from the plugins service doesn't look so good. In my defense, I was looking at the sonarqube_system_info.json and it reports:
"Plugins": {
"groovy": "1.5 [Groovy]",
"java": "5.0.1.12818 [SonarJava]",
"smells": "4.0.0 [Code Smells]",
"web": "2.5.0.476 [Web]",
"xml": "1.4.3.1027 [SonarXML]",
"clover": "3.1 [Clover]",
"scmmercurial": "1.1.1 [Mercurial]",
"Sonargraph": "3.5 [Sonargraph]",
"aemrules": "0.9 [AEM Rules for SonarQube]",
"checkstyle": "3.7 [Checkstyle]",
"javascript": "4.0.0.5862 [SonarJS]",
"status": "3.0.1 [SVG Badges]"
},

Answer 1

This issue is probably coming from a wrong usage of SonarQube, most probably by using multiple server on the same database.
See more details about how to detect this in thread : https://groups.google.com/forum/#!msg/sonarqube/IPjmDeGDUFc/dHMfJooXAQAJ