DatabaseInstanceStatusRetryPolicy.java

/*
 * Copyright 2013-2014 the original author or authors.
 *
 * Licensed 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.springframework.cloud.aws.jdbc.retry;


import com.amazonaws.services.rds.AmazonRDS;
import com.amazonaws.services.rds.model.DBInstance;
import com.amazonaws.services.rds.model.DBInstanceNotFoundException;
import com.amazonaws.services.rds.model.DescribeDBInstancesRequest;
import com.amazonaws.services.rds.model.DescribeDBInstancesResult;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.cloud.aws.core.env.ResourceIdResolver;
import org.springframework.retry.RetryContext;
import org.springframework.retry.RetryPolicy;
import org.springframework.retry.context.RetryContextSupport;
import org.springframework.util.Assert;

/**
 * {@link RetryPolicy} implementation that checks if it is useful to retry an operation based on the database instance
 * status. This class retrieves that database state and verifies through the {@link InstanceStatus} enum operation if
 * it is useful to retry the operation. This class does not retrieve the status if there is no Throwable registered to
 * avoid any performance implication during normal operations.
 * <p>This class should not be used alone because this would lead into a infinite retry, because this class does not
 * limit the amount of retries. Consider using this class together with the {@link SqlRetryPolicy} which limits the
 * maximum number of retries.</p>
 *
 * @author Agim Emruli
 * @since 1.0
 */
public class DatabaseInstanceStatusRetryPolicy implements RetryPolicy {

    /**
     * DB-Instance attribute name used inside the {@link RetryContext} to store the database instance name during the
     * retries.
     */
    private static final String DB_INSTANCE_ATTRIBUTE_NAME = "DbInstanceIdentifier";

    private static final Logger LOGGER = LoggerFactory.getLogger(DatabaseInstanceStatusRetryPolicy.class);

    /**
     * Database instance identifier which should be checked.
     */
    private final String dbInstanceIdentifier;

    /**
     * {@link AmazonRDS} client used to query the Amazon RDS service
     */
    private final AmazonRDS amazonRDS;

    private ResourceIdResolver resourceIdResolver;

    /**
     * Constructs this strategy implementation with it default and mandatory collaborators.
     *
     * @param amazonRDS
     *         - used to query the Amazon RDS service, must not be null
     * @param dbInstanceIdentifier
     *         - database instance for which this class should check the state.
     */
    public DatabaseInstanceStatusRetryPolicy(AmazonRDS amazonRDS, String dbInstanceIdentifier) {
        Assert.notNull(amazonRDS, "amazonRDS must not be null.");
        this.amazonRDS = amazonRDS;
        this.dbInstanceIdentifier = dbInstanceIdentifier;
    }

    /**
     * Configures an option {@link org.springframework.cloud.aws.core.env.ResourceIdResolver} to resolve logical name to physical name
     *
     * @param resourceIdResolver
     *         - the resourceIdResolver to be used, may be null
     */
    public void setResourceIdResolver(ResourceIdResolver resourceIdResolver) {
        this.resourceIdResolver = resourceIdResolver;
    }

    /**
     * Implementation that checks if there is an exception registered through {@link #registerThrowable(org.springframework.retry.RetryContext,
     * Throwable)}. Returns <code>true</code> if there is no exception registered at all and verifies the database instance status if
     * there is one registered.
     *
     * @param context
     *         - the retry context which may contain a registered exception
     * @return <code>true</code> if there is no exception registered or if there is a retry useful which is verified by the {@link
     * InstanceStatus} enum.
     */
    @Override
    public boolean canRetry(RetryContext context) {
        //noinspection ThrowableResultOfMethodCallIgnored
        return (context.getLastThrowable() == null || isDatabaseAvailable(context));
    }

    @Override
    public RetryContext open(RetryContext parent) {
        RetryContextSupport context = new RetryContextSupport(parent);
        context.setAttribute(DB_INSTANCE_ATTRIBUTE_NAME, getDbInstanceIdentifier());
        if (LOGGER.isTraceEnabled()) {
            LOGGER.trace("Starting RetryContext for database instance with identifier {}", getDbInstanceIdentifier());
        }
        return context;
    }

    @Override
    public void close(RetryContext context) {
        context.removeAttribute(DB_INSTANCE_ATTRIBUTE_NAME);
        if (LOGGER.isTraceEnabled()) {
            LOGGER.trace("Closing RetryContext for database instance with identifier {}", getDbInstanceIdentifier());
        }
    }

    @Override
    public void registerThrowable(RetryContext context, Throwable throwable) {
        ((RetryContextSupport) context).registerThrowable(throwable);
        if (LOGGER.isTraceEnabled()) {
            LOGGER.trace("Registered Throwable of Type {} for RetryContext", throwable.getClass().getName());
        }
    }

    private boolean isDatabaseAvailable(RetryContext context) {
        DescribeDBInstancesResult describeDBInstancesResult;
        try {
            describeDBInstancesResult = this.amazonRDS.describeDBInstances(new DescribeDBInstancesRequest().withDBInstanceIdentifier((String) context.getAttribute(DB_INSTANCE_ATTRIBUTE_NAME)));
        } catch (DBInstanceNotFoundException e) {
            LOGGER.warn("Database Instance with name {} has been removed or is not configured correctly, no retry possible", getDbInstanceIdentifier());
            //Database has been deleted while operating, hence we can not retry
            return false;
        }

        if (describeDBInstancesResult.getDBInstances().size() == 1) {
            DBInstance dbInstance = describeDBInstancesResult.getDBInstances().get(0);
            InstanceStatus instanceStatus = InstanceStatus.fromDatabaseStatus(dbInstance.getDBInstanceStatus());
            if (LOGGER.isTraceEnabled()) {
                LOGGER.trace("Status of database to be retried is {}", instanceStatus);
            }
            return instanceStatus.isRetryable();
        } else {
            throw new IllegalStateException("Multiple databases found for same identifier, this is likely an incompatibility with the Amazon SDK");
        }
    }

    private String getDbInstanceIdentifier() {
        return this.resourceIdResolver != null ? this.resourceIdResolver.resolveToPhysicalResourceId(this.dbInstanceIdentifier) : this.dbInstanceIdentifier;
    }
}