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/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.ha;
import java.io.IOException;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.CommonConfigurationKeys;
import org.apache.hadoop.ha.HAServiceProtocol.HAServiceState;
import org.apache.hadoop.ha.HAServiceProtocol.StateChangeRequestInfo;
import org.apache.hadoop.ha.HAServiceProtocol.RequestSource;
import org.apache.hadoop.ipc.RPC;
import org.apache.hadoop.thirdparty.com.google.common.base.Preconditions;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* The FailOverController is responsible for electing an active service
* on startup or when the current active is changing (eg due to failure),
* monitoring the health of a service, and performing a fail-over when a
* new active service is either manually selected by a user or elected.
*/
@InterfaceAudience.Private
@InterfaceStability.Evolving
public class FailoverController {
private static final Logger LOG =
LoggerFactory.getLogger(FailoverController.class);
private final int gracefulFenceTimeout;
private final int rpcTimeoutToNewActive;
private final Configuration conf;
/*
* Need a copy of conf for graceful fence to set
* configurable retries for IPC client.
* Refer HDFS-3561
*/
private final Configuration gracefulFenceConf;
private final RequestSource requestSource;
public FailoverController(Configuration conf,
RequestSource source) {
this.conf = conf;
this.gracefulFenceConf = new Configuration(conf);
this.requestSource = source;
this.gracefulFenceTimeout = getGracefulFenceTimeout(conf);
this.rpcTimeoutToNewActive = getRpcTimeoutToNewActive(conf);
//Configure less retries for graceful fence
int gracefulFenceConnectRetries = conf.getInt(
CommonConfigurationKeys.HA_FC_GRACEFUL_FENCE_CONNECTION_RETRIES,
CommonConfigurationKeys.HA_FC_GRACEFUL_FENCE_CONNECTION_RETRIES_DEFAULT);
gracefulFenceConf.setInt(
CommonConfigurationKeys.IPC_CLIENT_CONNECT_MAX_RETRIES_KEY,
gracefulFenceConnectRetries);
gracefulFenceConf.setInt(
CommonConfigurationKeys.IPC_CLIENT_CONNECT_MAX_RETRIES_ON_SOCKET_TIMEOUTS_KEY,
gracefulFenceConnectRetries);
}
static int getGracefulFenceTimeout(Configuration conf) {
return conf.getInt(
CommonConfigurationKeys.HA_FC_GRACEFUL_FENCE_TIMEOUT_KEY,
CommonConfigurationKeys.HA_FC_GRACEFUL_FENCE_TIMEOUT_DEFAULT);
}
static int getRpcTimeoutToNewActive(Configuration conf) {
return conf.getInt(
CommonConfigurationKeys.HA_FC_NEW_ACTIVE_TIMEOUT_KEY,
CommonConfigurationKeys.HA_FC_NEW_ACTIVE_TIMEOUT_DEFAULT);
}
/**
* Perform pre-failover checks on the given service we plan to
* failover to, eg to prevent failing over to a service (eg due
* to it being inaccessible, already active, not healthy, etc).
*
* An option to ignore toSvc if it claims it is not ready to
* become active is provided in case performing a failover will
* allow it to become active, eg because it triggers a log roll
* so the standby can learn about new blocks and leave safemode.
*
* @param from currently active service
* @param target service to make active
* @param forceActive ignore toSvc if it reports that it is not ready
* @throws FailoverFailedException if we should avoid failover
*/
private void preFailoverChecks(HAServiceTarget from,
HAServiceTarget target,
boolean forceActive)
throws FailoverFailedException {
HAServiceStatus toSvcStatus;
HAServiceProtocol toSvc;
if (from.getAddress().equals(target.getAddress())) {
throw new FailoverFailedException(
"Can't failover a service to itself");
}
try {
toSvc = target.getProxy(conf, rpcTimeoutToNewActive);
toSvcStatus = toSvc.getServiceStatus();
} catch (IOException e) {
String msg = "Unable to get service state for " + target;
LOG.error(msg, e);
throw new FailoverFailedException(msg, e);
}
if (!toSvcStatus.getState().equals(HAServiceState.STANDBY)) {
throw new FailoverFailedException(
"Can't failover to an " + toSvcStatus.getState() + " service");
}
if (!toSvcStatus.isReadyToBecomeActive()) {
String notReadyReason = toSvcStatus.getNotReadyReason();
if (!forceActive) {
throw new FailoverFailedException(
target + " is not ready to become active: " +
notReadyReason);
} else {
LOG.warn("Service is not ready to become active, but forcing: {}",
notReadyReason);
}
}
try {
HAServiceProtocolHelper.monitorHealth(toSvc, createReqInfo());
} catch (HealthCheckFailedException hce) {
throw new FailoverFailedException(
"Can't failover to an unhealthy service", hce);
} catch (IOException e) {
throw new FailoverFailedException(
"Got an IO exception", e);
}
}
private StateChangeRequestInfo createReqInfo() {
return new StateChangeRequestInfo(requestSource);
}
/**
* Try to get the HA state of the node at the given address. This
* function is guaranteed to be "quick" -- ie it has a short timeout
* and no retries. Its only purpose is to avoid fencing a node that
* has already restarted.
*/
boolean tryGracefulFence(HAServiceTarget svc) {
HAServiceProtocol proxy = null;
try {
proxy = svc.getProxy(gracefulFenceConf, gracefulFenceTimeout);
proxy.transitionToStandby(createReqInfo());
return true;
} catch (ServiceFailedException sfe) {
LOG.warn("Unable to gracefully make {} standby ({})",
svc, sfe.getMessage());
} catch (IOException ioe) {
LOG.warn("Unable to gracefully make {} standby (unable to connect)",
svc, ioe);
} finally {
if (proxy != null) {
RPC.stopProxy(proxy);
}
}
return false;
}
/**
* Failover from service 1 to service 2. If the failover fails
* then try to failback.
*
* @param fromSvc currently active service
* @param toSvc service to make active
* @param forceFence to fence fromSvc even if not strictly necessary
* @param forceActive try to make toSvc active even if it is not ready
* @throws FailoverFailedException if the failover fails
*/
public void failover(HAServiceTarget fromSvc,
HAServiceTarget toSvc,
boolean forceFence,
boolean forceActive)
throws FailoverFailedException {
Preconditions.checkArgument(fromSvc.getFencer() != null,
"failover requires a fencer");
preFailoverChecks(fromSvc, toSvc, forceActive);
// Try to make fromSvc standby
boolean tryFence = true;
if (tryGracefulFence(fromSvc)) {
tryFence = forceFence;
}
// Fence fromSvc if it's required or forced by the user
if (tryFence) {
if (!fromSvc.getFencer().fence(fromSvc, toSvc)) {
throw new FailoverFailedException("Unable to fence " +
fromSvc + ". Fencing failed.");
}
}
// Try to make toSvc active
boolean failed = false;
Throwable cause = null;
try {
HAServiceProtocolHelper.transitionToActive(
toSvc.getProxy(conf, rpcTimeoutToNewActive),
createReqInfo());
} catch (ServiceFailedException sfe) {
LOG.error("Unable to make {} active ({}). Failing back.",
toSvc, sfe.getMessage());
failed = true;
cause = sfe;
} catch (IOException ioe) {
LOG.error("Unable to make {} active (unable to connect). Failing back.",
toSvc, ioe);
failed = true;
cause = ioe;
}
// We failed to make toSvc active
if (failed) {
String msg = "Unable to failover to " + toSvc;
// Only try to failback if we didn't fence fromSvc
if (!tryFence) {
try {
// Unconditionally fence toSvc in case it is still trying to
// become active, eg we timed out waiting for its response.
// Unconditionally force fromSvc to become active since it
// was previously active when we initiated failover.
failover(toSvc, fromSvc, true, true);
} catch (FailoverFailedException ffe) {
msg += ". Failback to " + fromSvc +
" failed (" + ffe.getMessage() + ")";
LOG.error(msg);
}
}
throw new FailoverFailedException(msg, cause);
}
}
}
