[KNOX-1165] Another unnamed CacheManager already exists in the same VM

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 0.12.0, 0.13.0, 0.14.0, 1.0.0, 1.1.0
• Fix Version/s: 1.2.0
• Component/s: Server, Site
• Environment: JDK 1.8 ; CentOS-6 (64bit)
• Assignee: Kevin Risden
• Reporter: Ernani Pereira de Mattos Junior
• Created: 09/Jan/18 15:41
• Updated: 28/Mar/19 13:57
• Resolved: 16/Nov/18 15:07

Description

Solution: See updated documentation here: https://knox.apache.org/books/knox-1-2-0/user-guide.html#LDAP+Authentication+Caching

Ensure that the following is set:

<param>
    <name>main.cacheManager</name>
    <value>org.apache.knox.gateway.shirorealm.KnoxCacheManager</value>
</param>

Problem

Issue is described on the note "Error:Shiro environment initialization failed" when starting Knox;

ERROR env.EnvironmentLoader (EnvironmentLoader.java:initEnvironment(146)) - Shiro environment initialization failed
 org.apache.shiro.cache.CacheException: net.sf.ehcache.CacheException: Another unnamed CacheManager already exists in the same VM. Please provide unique names for each CacheManager in the config or do one of following 

After implementing the solution of creating a new ehcache.xml and reference as <ehcache name="knox-mytopology1"> we still see the issue:

Caused by: net.sf.ehcache.CacheException: Another CacheManager with same name 'knox-tp' already exists in the same VM. Please provide unique names for each CacheManager in the config or do one of following: 

Steps to reproduce

When enabling the following parameters: 

<param>
  <name>main.cacheManager</name>
  <value>org.apache.shiro.cache.ehcache.EhCacheManager</value>
</param>
<param>
  <name>main.securityManager.cacheManager</name>
  <value>$cacheManager</value>
</param>
<param>
  <name>main.ldapRealm.authenticationCachingEnabled</name>
  <value>true</value>
</param>

More Info

This KNOX-804 was open to solve this same issue but is not documented anywhere, but we can see the coding changes in GitHub.

• The issue seems to be a racing condition on the Shiro lib class, in which depending on the processing power of the server there are two threads within the same "if" statement;
  • ref: https://github.com/apache/shiro/blob/master/support/ehcache/src/main/java/org/apache/shiro/cache/ehcache/EhCacheManager.java
• The Default constructor only builds the Object, and does not do much: 

• /**Default no argument constructor*/
   public EhCacheManager() {
   }

• Accordingly with shiro documentation: 

  • /**
    Initializes this instance.
    <p/>
    If a {@link #setCacheManager CacheManager} has been explicitly set (e.g. via Dependency Injection or programmatically) prior to calling this
    method, this method does nothing.
    <p/>
    However, if no {@code CacheManager} has been set, the default Ehcache singleton will be initialized, where Ehcache will look for an {@code ehcache.xml} file at the root of the classpath. If one is not found, Ehcache will use its own failsafe configuration file.
    <p/>
    Because Shiro cannot use the failsafe defaults (fail-safe expunges cached objects after 2 minutes, something not desirable for Shiro sessions), this class manages an internal default configuration for this case.
    
    @throws org.apache.shiro.cache.CacheException if there are any CacheExceptions thrown by EhCache.
    @see net.sf.ehcache.CacheManager#create
     */
    public final void init() throws CacheException { ensureCacheManager(); }
    
    private net.sf.ehcache.CacheManager ensureCacheManager()
    { ***It fails in here. }

• This is the head of the exception: The source of the existing CacheManager is:

  • InputStreamConfigurationSource [stream=java.io.BufferedInputStream@675ffd1d] at org.apache.shiro.cache.ehcache.EhCacheManager.ensureCacheManager(EhCacheManager.java:224) at org.apache.shiro.cache.ehcache.EhCacheManager.init(EhCacheManager.java:199) at org.apache.shiro.util.LifecycleUtils.init(LifecycleUtils.java:45) at org.apache.shiro.util.LifecycleUtils.init(LifecycleUtils.java:40)

• Starting from KNOX-804, the KnoxCacheManager was introduced. Remember that Init() will do nothing if anything in case the setCacheManager is explicitly set.
  • ref: https://github.com/apache/knox/commit/f9d8e07d768459240c8665f139cc140575dc5216

Issue Links

• relates to: KNOX-804 Knox ehcache usage has intermittent CacheManger exception