I am getting the follow stack trace from the logs when 4.5.0.Final tries to start on 2 of my Keycloak cluster (thankfully both non-production): 00:42:40,128 WARN [org.jboss.modules.define] (main) Failed to define class org.jboss.as.server.BootstrapImpl$ShutdownHook in Module "org.jboss.as.server" version 5.0.0.Final from local module loader @2b95e48b (finder: local module finde r @4a3329b9 (roots: /opt/jboss/keycloak/modules,/opt/jboss/keycloak/modules/system/layers/keycloak,/opt/jboss/keycloak/modules/system/layers/base)): java.lang.NoClassDefFoundError: Failed to link org/jboss/as/server/BootstrapImpl$Shutdow nHook (Module "org.jboss.as.server" version 5.0.0.Final from local module loader @2b95e48b (finder: local module finder @4a3329b9 (roots: /opt/jboss/keycloak/modules,/opt/jboss/keycloak/modules/system/layers/keycloak,/opt/jboss/keycloak/ modules/system/layers/base))): datadog/trace/agent/tooling/context/FieldBackedProvider$ContextAccessor$java$lang$Runnable$datadog$trace$bootstrap$instrumentation$java$concurrent$State at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:763) at org.jboss.modules.ModuleClassLoader.doDefineOrLoadClass(ModuleClassLoader.java:423) at org.jboss.modules.ModuleClassLoader.defineClass(ModuleClassLoader.java:519) at org.jboss.modules.ModuleClassLoader.loadClassLocal(ModuleClassLoader.java:339) at org.jboss.modules.ModuleClassLoader$1.loadClassLocal(ModuleClassLoader.java:126) at org.jboss.modules.Module.loadModuleClass(Module.java:731) at org.jboss.modules.ModuleClassLoader.findClass(ModuleClassLoader.java:247) at org.jboss.modules.ConcurrentClassLoader.performLoadClassUnchecked(ConcurrentClassLoader.java:410) at org.jboss.modules.ConcurrentClassLoader.performLoadClass(ConcurrentClassLoader.java:398) at org.jboss.modules.ConcurrentClassLoader.loadClass(ConcurrentClassLoader.java:116) at org.jboss.as.server.BootstrapImpl.<init>(BootstrapImpl.java:67) at org.jboss.as.server.Bootstrap$Factory.newInstance(Bootstrap.java:275) at org.jboss.as.server.Main.main(Main.java:105) at org.jboss.modules.Module.run(Module.java:352) at org.jboss.modules.Module.run(Module.java:320) at org.jboss.modules.Main.main(Main.java:593) java.lang.NoClassDefFoundError: Failed to link org/jboss/as/server/BootstrapImpl$ShutdownHook (Module "org.jboss.as.server" version 5.0.0.Final from local module loader @2b95e48b (finder: local module finder @4a3329b9 (roots: /opt/jboss/ keycloak/modules,/opt/jboss/keycloak/modules/system/layers/keycloak,/opt/jboss/keycloak/modules/system/layers/base))): datadog/trace/agent/tooling/context/FieldBackedProvider$ContextAccessor$java$lang$Runnable$datadog$trace$bootstrap$ins trumentation$java$concurrent$State at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:763) at org.jboss.modules.ModuleClassLoader.doDefineOrLoadClass(ModuleClassLoader.java:423) at org.jboss.modules.ModuleClassLoader.defineClass(ModuleClassLoader.java:519) at org.jboss.modules.ModuleClassLoader.loadClassLocal(ModuleClassLoader.java:339) at org.jboss.modules.ModuleClassLoader$1.loadClassLocal(ModuleClassLoader.java:126) at org.jboss.modules.Module.loadModuleClass(Module.java:731) at org.jboss.modules.ModuleClassLoader.findClass(ModuleClassLoader.java:247) at org.jboss.modules.ConcurrentClassLoader.performLoadClassUnchecked(ConcurrentClassLoader.java:410) at org.jboss.modules.ConcurrentClassLoader.performLoadClass(ConcurrentClassLoader.java:398) at org.jboss.modules.ConcurrentClassLoader.loadClass(ConcurrentClassLoader.java:116) at org.jboss.as.server.BootstrapImpl.<init>(BootstrapImpl.java:67) at org.jboss.as.server.Bootstrap$Factory.newInstance(Bootstrap.java:275) at org.jboss.as.server.Main.main(Main.java:105) at org.jboss.modules.Module.run(Module.java:352) at org.jboss.modules.Module.run(Module.java:320) at org.jboss.modules.Main.main(Main.java:593) 00:42:40,251 FATAL [org.jboss.as.server] (main) WFLYSRV0239: Aborting with exit code 1 Thankfully my production cluster is up at the moment but I fear that if it restarts (for whatever reason) it too will fail. Anyone else seen and solve this one? For the record, I am already looking at upgrading to 4.7.0.Final but that has it's own set of issues that I am currently working through. Best regards, Graham Burgess RΛZΞR|stormmore Sr. DevOps Engineer (USA) Email: graham.burgess(a)razer.com DID: (415) 374 0639 [http://assets.razerzone.com/email/email-sig.jpg] Razer.com<https://www.razer.com/> | Razer Game Store<https://gamestore.razer.com/> | Razer Insider<https://insider.razer.com/> | Razer zVault<https://zvault.razer.com/> [https://upload.wikimedia.org/wikipedia/commons/thumb/c/c2/F_icon.svg/200p... [Twitter_Social_Icon_Rounded_Square_Color] <https://twitter.com/Razer> [glyph-logo_May2016] <https://www.instagram.com/razer/> [youtube_social_squircle_red] <https://www.youtube.com/Razer?sub_confirmation=1> Razer Inc. (San Francisco) 201 3rd Street, Suite 900 San Francisco CA 94103, USA Tel: +1 (415) 266 5300 Razer Inc. 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