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failover2 on connect #1133

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Oct 3, 2024
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failover2 on connect #1133

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88 changes: 84 additions & 4 deletions wrapper/src/main/java/software/amazon/jdbc/plugin/failover2/FailoverConnectionPlugin.java
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Original file line number Diff line number Diff line change
Expand Up @@ -43,6 +43,7 @@
import software.amazon.jdbc.plugin.staledns.AuroraStaleDnsHelper;
import software.amazon.jdbc.targetdriverdialect.TargetDriverDialect;
import software.amazon.jdbc.util.Messages;
import software.amazon.jdbc.util.PropertyUtils;
import software.amazon.jdbc.util.RdsUrlType;
import software.amazon.jdbc.util.RdsUtils;
import software.amazon.jdbc.util.SqlState;
Expand All @@ -65,6 +66,8 @@ public class FailoverConnectionPlugin extends AbstractConnectionPlugin {
private static final String TELEMETRY_WRITER_FAILOVER = "failover to writer node";
private static final String TELEMETRY_READER_FAILOVER = "failover to replica";

private static final String INTERNAL_CONNECT_PROPERTY_NAME = "76c06979-49c4-4c86-9600-a63605b83f50";

public static final AwsWrapperProperty FAILOVER_TIMEOUT_MS =
new AwsWrapperProperty(
"failoverTimeoutMs",
Expand All @@ -87,10 +90,18 @@ public class FailoverConnectionPlugin extends AbstractConnectionPlugin {
"random",
"The strategy that should be used to select a new reader host while opening a new connection.");

public static final AwsWrapperProperty ENABLE_CONNECT_FAILOVER =
new AwsWrapperProperty(
"enableConnectFailover", "false",
"Enable/disable cluster-aware failover if the initial connection to the database fails due to a "
+ "network exception. Note that this may result in a connection to a different instance in the cluster "
+ "than was specified by the URL.");

private static final Set<String> subscribedMethods =
Collections.unmodifiableSet(new HashSet<String>() {
{
addAll(SubscribedMethodHelper.NETWORK_BOUND_METHODS);
add("connect");
add("initHostProvider");
}
});
Expand Down Expand Up @@ -317,7 +328,6 @@ protected <E extends Exception> void dealWithIllegalStateException(
* @throws SQLException if an error occurs
*/
protected void failover(final HostSpec failedHost) throws SQLException {
this.pluginService.setAvailability(failedHost.asAliases(), HostAvailability.NOT_AVAILABLE);
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if (this.failoverMode == FailoverMode.STRICT_WRITER) {
failoverWriter();
Expand Down Expand Up @@ -364,6 +374,9 @@ protected void failoverReader() throws SQLException {
throw new FailoverFailedSQLException(Messages.get("Failover.unableToConnectToReader"));
}

final Properties copyProp = PropertyUtils.copyProperties(this.properties);
copyProp.setProperty(INTERNAL_CONNECT_PROPERTY_NAME, "true");

final List<HostSpec> hosts = this.pluginService.getHosts();
Connection readerCandidateConn = null;
HostSpec readerCandidate = null;
Expand All @@ -389,7 +402,7 @@ protected void failoverReader() throws SQLException {
}

try {
readerCandidateConn = this.pluginService.connect(readerCandidate, this.properties);
readerCandidateConn = this.pluginService.connect(readerCandidate, copyProp);
if (this.pluginService.getHostRole(readerCandidateConn) != HostRole.READER) {
readerCandidateConn.close();
readerCandidateConn = null;
Expand All @@ -412,7 +425,7 @@ protected void failoverReader() throws SQLException {
this.failoverReaderHostSelectorStrategySetting);
if (readerCandidate != null) {
try {
readerCandidateConn = this.pluginService.connect(readerCandidate, this.properties);
readerCandidateConn = this.pluginService.connect(readerCandidate, copyProp);
} catch (SQLException ex) {
readerCandidate = null;
}
Expand Down Expand Up @@ -480,6 +493,8 @@ protected void failoverWriter() throws SQLException {
}

final List<HostSpec> updatedHosts = this.pluginService.getHosts();
final Properties copyProp = PropertyUtils.copyProperties(this.properties);
copyProp.setProperty(INTERNAL_CONNECT_PROPERTY_NAME, "true");

Connection writerCandidateConn = null;
final HostSpec writerCandidate = updatedHosts.stream()
Expand All @@ -489,7 +504,7 @@ protected void failoverWriter() throws SQLException {

if (writerCandidate != null) {
try {
writerCandidateConn = this.pluginService.connect(writerCandidate, this.properties);
writerCandidateConn = this.pluginService.connect(writerCandidate, copyProp);
} catch (SQLException ex) {
// do nothing
}
Expand Down Expand Up @@ -606,4 +621,69 @@ protected boolean canDirectExecute(final String methodName) {
|| methodName.equals(METHOD_IS_CLOSED)
|| methodName.equals(METHOD_ABORT));
}

@Override
public Connection connect(
final String driverProtocol,
final HostSpec hostSpec,
final Properties props,
final boolean isInitialConnection,
final JdbcCallable<Connection, SQLException> connectFunc)
throws SQLException {

if (!ENABLE_CONNECT_FAILOVER.getBoolean(props)) {
return connectFunc.call();
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Shouldn't we be connecting using getVerifiedConnection in this case?

Suggested change
return connectFunc.call();
return this.staleDnsHelper.getVerifiedConnection(isInitialConnection, this.hostListProviderService,
driverProtocol, hostSpec, props, connectFunc);

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getVerifiedConnection() call already been made of a caller of connect() that is the same failover2 plugin. I don't think we need to execute it again.

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sorry are you saying that getVerifiedConnection has been previously called by another plugin or previously called by failover2?

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failover2 connect() is called, then getVerifiedConnection() is called.

aws-advanced-jdbc-wrapper/wrapper/src/main/java/software/amazon/jdbc/plugin/failover2/FailoverConnectionPlugin.java

Line 654 in b84d66c

conn = this.staleDnsHelper.getVerifiedConnection(isInitialConnection, this.hostListProviderService,

After that, if connection isn't established, a failover starts.

aws-advanced-jdbc-wrapper/wrapper/src/main/java/software/amazon/jdbc/plugin/failover2/FailoverConnectionPlugin.java

Line 664 in b84d66c

this.failover(hostSpec);

And eventually it calls pluginService.connect()

aws-advanced-jdbc-wrapper/wrapper/src/main/java/software/amazon/jdbc/plugin/failover2/FailoverConnectionPlugin.java

Line 507 in b84d66c

writerCandidateConn = this.pluginService.connect(writerCandidate, copyProp);

that will call failover2 connect() again. This call can be passed through to the next plugin since it's already been handled earlier.

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@aaron-congo aaron-congo Oct 3, 2024 •
edited
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If I understand correctly that explains why we should use connectFunc.call instead of getVerifiedConnection when the props contain the INTERNAL_CONNECT_PROPERTY_NAME property, but this particular line is covering a different scenario: it is hit when connect failover is disabled. When connect failover is disabled we will never enter the failover logic below, so as the code currently is written, getVerifiedConnection will never be called in this scenario

}

// This call was initiated by this failover2 plugin and doesn't require any additional processing.
if (props.containsKey(INTERNAL_CONNECT_PROPERTY_NAME)) {
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Would it work to change this condition to the following so that we don't have to add the INTERNAL_CONNECT_PROPERTY_NAME? I think calling forceConnect probably always indicates we just want to connect directly without any special additional logic. If this works, we can probably just get rid of connectInternal and have different implementations for connect vs forceConnect.

Suggested change
if (props.containsKey(INTERNAL_CONNECT_PROPERTY_NAME)) {
if (isForceConnect)) {

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forceConnect() is for direct connection but it's not used in failover2. So forceConnect() makes not much sense to this case. Also, failover2 uses regular connect() because MonitoringHostListProvider already verified topology so no need to force direct connect. And with a regular connect(), the call comes to failover2 plugin again and our intention is to skip it.

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I see. Using the INTERNAL_CONNECT_PROPERTY_NAME property as a flag seems a bit hacky/strange to me but I can't think of an alternative at the moment.

return connectFunc.call();
}

Connection conn = null;

final HostSpec hostSpecWithAvailability = this.pluginService.getHosts().stream()
.filter(x -> x.getHostAndPort().equals(hostSpec.getHostAndPort()))
.findFirst()
.orElse(null);

if (hostSpecWithAvailability == null
|| hostSpecWithAvailability.getAvailability() != HostAvailability.NOT_AVAILABLE) {

try {
conn = this.staleDnsHelper.getVerifiedConnection(isInitialConnection, this.hostListProviderService,
driverProtocol, hostSpec, props, connectFunc);
} catch (final SQLException e) {
if (!this.shouldExceptionTriggerConnectionSwitch(e)) {
throw e;
}

this.pluginService.setAvailability(hostSpec.asAliases(), HostAvailability.NOT_AVAILABLE);

try {
this.failover(hostSpec);
} catch (FailoverSuccessSQLException failoverSuccessException) {
conn = this.pluginService.getCurrentConnection();
}
}
} else {
try {
this.pluginService.refreshHostList();
this.failover(hostSpec);
} catch (FailoverSuccessSQLException failoverSuccessException) {
conn = this.pluginService.getCurrentConnection();
}
}

if (conn == null) {
// This should be unreachable, the above logic will either get a connection successfully or throw an exception.
throw new SQLException(Messages.get("Failover.unableToConnect"));
}

if (isInitialConnection) {
this.pluginService.refreshHostList(conn);
}

return conn;
}
}
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