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| <h2 title="Interface ActiveStandbyElector.ActiveStandbyElectorCallback" class="title">Interface ActiveStandbyElector.ActiveStandbyElectorCallback</h2> |
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| <dd>org.apache.hadoop.ha.ActiveStandbyElector</dd> |
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| <pre>public static interface <span class="typeNameLabel">ActiveStandbyElector.ActiveStandbyElectorCallback</span></pre> |
| <div class="block">Callback interface to interact with the ActiveStandbyElector object. <br> |
| The application will be notified with a callback only on state changes |
| (i.e. there will never be successive calls to becomeActive without an |
| intermediate call to enterNeutralMode). <br> |
| The callbacks will be running on Zookeeper client library threads. The |
| application should return from these callbacks quickly so as not to impede |
| Zookeeper client library performance and notifications. The app will |
| typically remember the state change and return from the callback. It will |
| then proceed with implementing actions around that state change. It is |
| possible to be called back again while these actions are in flight and the |
| app should handle this scenario.</div> |
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| <table class="memberSummary" border="0" cellpadding="3" cellspacing="0" summary="Method Summary table, listing methods, and an explanation"> |
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| <td class="colFirst"><code>void</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../org/apache/hadoop/ha/ActiveStandbyElector.ActiveStandbyElectorCallback.html#becomeActive--">becomeActive</a></span>()</code> |
| <div class="block">This method is called when the app becomes the active leader.</div> |
| </td> |
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| <td class="colFirst"><code>void</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../org/apache/hadoop/ha/ActiveStandbyElector.ActiveStandbyElectorCallback.html#becomeStandby--">becomeStandby</a></span>()</code> |
| <div class="block">This method is called when the app becomes a standby</div> |
| </td> |
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| <td class="colFirst"><code>void</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../org/apache/hadoop/ha/ActiveStandbyElector.ActiveStandbyElectorCallback.html#enterNeutralMode--">enterNeutralMode</a></span>()</code> |
| <div class="block">If the elector gets disconnected from Zookeeper and does not know about |
| the lock state, then it will notify the service via the enterNeutralMode |
| interface.</div> |
| </td> |
| </tr> |
| <tr id="i3" class="rowColor"> |
| <td class="colFirst"><code>void</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../org/apache/hadoop/ha/ActiveStandbyElector.ActiveStandbyElectorCallback.html#fenceOldActive-byte:A-">fenceOldActive</a></span>(byte[] oldActiveData)</code> |
| <div class="block">If an old active has failed, rather than exited gracefully, then |
| the new active may need to take some fencing actions against it |
| before proceeding with failover.</div> |
| </td> |
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| <td class="colFirst"><code>void</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../org/apache/hadoop/ha/ActiveStandbyElector.ActiveStandbyElectorCallback.html#notifyFatalError-java.lang.String-">notifyFatalError</a></span>(<a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a> errorMessage)</code> |
| <div class="block">If there is any fatal error (e.g.</div> |
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| <h4>becomeActive</h4> |
| <pre>void becomeActive() |
| throws <a href="../../../../org/apache/hadoop/ha/ServiceFailedException.html" title="class in org.apache.hadoop.ha">ServiceFailedException</a></pre> |
| <div class="block">This method is called when the app becomes the active leader. |
| If the service fails to become active, it should throw |
| ServiceFailedException. This will cause the elector to |
| sleep for a short period, then re-join the election. |
| |
| Callback implementations are expected to manage their own |
| timeouts (e.g. when making an RPC to a remote node).</div> |
| <dl> |
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| <dd><code><a href="../../../../org/apache/hadoop/ha/ServiceFailedException.html" title="class in org.apache.hadoop.ha">ServiceFailedException</a></code></dd> |
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| <h4>becomeStandby</h4> |
| <pre>void becomeStandby()</pre> |
| <div class="block">This method is called when the app becomes a standby</div> |
| </li> |
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| <h4>enterNeutralMode</h4> |
| <pre>void enterNeutralMode()</pre> |
| <div class="block">If the elector gets disconnected from Zookeeper and does not know about |
| the lock state, then it will notify the service via the enterNeutralMode |
| interface. The service may choose to ignore this or stop doing state |
| changing operations. Upon reconnection, the elector verifies the leader |
| status and calls back on the becomeActive and becomeStandby app |
| interfaces. <br> |
| Zookeeper disconnects can happen due to network issues or loss of |
| Zookeeper quorum. Thus enterNeutralMode can be used to guard against |
| split-brain issues. In such situations it might be prudent to call |
| becomeStandby too. However, such state change operations might be |
| expensive and enterNeutralMode can help guard against doing that for |
| transient issues.</div> |
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| <h4>notifyFatalError</h4> |
| <pre>void notifyFatalError(<a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a> errorMessage)</pre> |
| <div class="block">If there is any fatal error (e.g. wrong ACL's, unexpected Zookeeper |
| errors or Zookeeper persistent unavailability) then notifyFatalError is |
| called to notify the app about it.</div> |
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| <h4>fenceOldActive</h4> |
| <pre>void fenceOldActive(byte[] oldActiveData)</pre> |
| <div class="block">If an old active has failed, rather than exited gracefully, then |
| the new active may need to take some fencing actions against it |
| before proceeding with failover.</div> |
| <dl> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>oldActiveData</code> - the application data provided by the prior active</dd> |
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