This topic describes how to configure two-way data synchronization between ApsaraDB for Redis Enhanced Edition instances by using Data Transmission Service (DTS). The data synchronization feature is applicable to scenarios such as active geo-redundancy and geo-disaster recovery.

Prerequisites

The source and destination instances are ApsaraDB for Redis Enhanced Edition instances (version 5.0). For more information, see the ApsaraDB for Redis Enhanced Edition documentation.
Note ApsaraDB for Redis Enhanced Edition supports the cluster, standard, and read/write splitting architectures.

Precautions

  • During two-way data synchronization, the data synchronization task in one direction performs initial full data synchronization and incremental data migration. The data synchronization task in the opposite direction performs only incremental data synchronization.
    Warning To ensure data consistency, do not modify or write data to the same key in the source and destination databases while the two-way data synchronization task is running.
  • DTS uses resources of the source and destination databases during initial full data synchronization. This may increase the load of the database server. If the data volume is large or the specification is low, database services may become unavailable. Before you synchronize data, evaluate the performance of the source and destination databases. We recommend that you synchronize data during off-peak hours.
  • We recommend that you do not run the FLUSHDB or FLUSHALL command in the source instance. Otherwise, data may be inconsistent between the source and destination instances.
  • If the data eviction policy (maxmemory-policy) of the destination database is not set to noeviction, the data between the source and destination databases may become inconsistent. For more information about the data eviction policy, see How does ApsaraDB for Redis evict data by default?
  • If direct connection is disabled for the destination ApsaraDB for Redis instance, DTS uses the proxy forwarding mode to write data to the destination instance.
    Note For more information, see Enable a direct connection.

Operations that can be synchronized

  • APPEND
  • BITOP, BLPOP, BRPOP, and BRPOPLPUSH
  • DECR, DECRBY, and DEL
  • EVAL, EVALSHA, EXEC, EXPIRE, and EXPIREAT
  • GEOADD and GETSET
  • HDEL, HINCRBY, HINCRBYFLOAT, HMSET, HSET, and HSETNX
  • INCR, INCRBY, and INCRBYFLOAT
  • LINSERT, LPOP, LPUSH, LPUSHX, LREM, LSET, and LTRIM
  • MOVE, MSET, MSETNX, and MULTI
  • PERSIST, PEXPIRE, PEXPIREAT, PFADD, PFMERGE, PSETEX, and PUBLISH
  • RENAME, RENAMENX, RESTORE, RPOP, RPOPLPUSH, RPUSH, and RPUSHX
  • SADD, SDIFFSTORE, SELECT, SET, SETBIT, SETEX, SETNX, SETRANGE, SINTERSTORE, SMOVE, SPOP, SREM, and SUNIONSTORE
  • ZADD, ZINCRBY, ZINTERSTORE, ZREM, ZREMRANGEBYLEX, ZUNIONSTORE, ZREMRANGEBYRANK, and ZREMRANGEBYSCORE
  • SWAPDB (This operation is not supported if the source or destination Redis instance is deployed in the cluster architecture.)
Notice
  • If you use the EVAL or EVALSHA command to call Lua scripts, DTS cannot identify whether these Lua scripts are executed on the destination database. During incremental data synchronization, the destination database does not explicitly return the execution results of Lua scripts.
  • When calling the SYNC or PSYNC command to transfer data of the LIST type, DTS does not clear the existing data. In this case, the destination database may contain duplicate data records.

Procedure

  1. Purchase a data synchronization instance. For more information, see Purchase procedure.
    Notice On the buy page, set Source Instance to Redis, set Target Instance to Redis, and set Synchronization Topology to Two-Way Synchronization.
  2. Log on to the DTS console.
  3. In the left-side navigation pane, click Data Synchronization.
  4. At the top of the Synchronization Tasks page, select the region where the destination instance resides.
    Select a region
  5. Configure the data synchronization task in one direction.
    1. Find the data synchronization instance, and click Configure Synchronization Channel in the Actions column of the first data synchronization task.
      Notice A two-way data synchronization instance contains two data synchronization tasks. You must configure a channel for each task. When you configure the second data synchronization task, find the task and click Configure Synchronization Channel in the Actions column.
      Two-way data synchronization tasks
    2. Configure the source and destination instances.
      Configure the source and destination instances
      Section Parameter Description
      N/A Synchronization Task Name DTS automatically generates a task name. We recommend that you specify an informative name for easy identification. You do not need to use a unique task name.
      Source Instance Details Instance Type Select Redis Instance.
      Instance Region The region of the source instance. The region is the same as the source region that you selected when you purchased the data synchronization instance. You cannot change the value of this parameter.
      Instance ID Select the ID of the source ApsaraDB for Redis instance.
      Notice When you configure the data synchronization task in the opposite direction, select the ID of the destination ApsaraDB for Redis instance.
      Database Password The database password of the source ApsaraDB for Redis instance.
      Notice The format of the database password is <user>:<password>. For example, if the username of the custom account is admin and the password is Rp829dlwa, the database password is admin:Rp829dlwa.
      Destination Instance Details Instance Type Select Redis Instance.
      Instance Region The region of the destination instance. The region is the same as the destination region that you selected when you purchased the data synchronization instance. You cannot change the value of this parameter.
      Instance ID Select the ID of the destination ApsaraDB for Redis instance.
      Notice When you configure the data synchronization task in the opposite direction, select the ID of the source ApsaraDB for Redis instance.
      Database Password The database password of the destination ApsaraDB for Redis instance.
      Notice The format of the database password is <user>:<password>. For example, if the username of the custom account is admin and the password is Rp829dlwa, the database password is admin:Rp829dlwa.
    3. In the lower-right corner of the page, click Set Whitelist and Next.
      DTS adds the CIDR blocks of DTS servers to the whitelists of the source and destination ApsaraDB for Redis instances. This ensures that DTS servers can connect to the source and destination instances.
    4. Configure the synchronization policy and objects.
      Select objects for two-way data synchronization between ApsaraDB for Redis instances
      Section Parameter Description
      Synchronization policy Conflict Resolution Policy Overwrite

      During data synchronization, if data records have the same key but different values, the data record with the latest key value overwrites the conflicting records.

      Processing Mode In Existed Target Table
      • Pre-check and Intercept: checks whether the destination database is empty. If the destination database is empty, the precheck is passed. If the database is not empty, an error is returned during the precheck and the data synchronization task cannot be started.
      • Ignore: skips the check for empty destination database.
        Warning If you select Ignore, the data records in the source database overwrite the data records with the same keys in the destination database.
      Objects to be synchronized N/A
      • Select a database from the Available section and click the Right arrow icon to move the database to the Selected section.
      • You can select only databases as the objects to be synchronized. You cannot select keys as the objects to be synchronized.
    5. In the lower-right corner of the page, click Next.
    6. Configure initial synchronization.
      Configure initial synchronization between ApsaraDB for Redis instances

      The value is set to Include full data + incremental data. DTS synchronizes historical data from the source ApsaraDB for Redis instance to the destination ApsaraDB for Redis instance. Then, DTS synchronizes incremental data.

      Notice If all the required objects have been synchronized from the source instance to the destination instance, the data synchronization task in the opposite direction synchronizes only incremental data.
    7. In the lower-right corner of the page, click Precheck.
      Note
      • Before you can start the data synchronization task, a precheck is performed. You can start the data synchronization task only after the task passes the precheck.
      • If the task fails to pass the precheck, click the Info icon icon next to each failed item to view details. Troubleshoot the issues based on the causes and run the precheck again.
    8. Close the Precheck dialog box after the following message is displayed: The precheck is passed. Then, the first data synchronization task starts.
  6. Wait until the initial synchronization is complete and the data synchronization task is in the Synchronizing state.
    You can view the status of the data synchronization task on the Synchronization Tasks page.
  7. Configure the data synchronization task in the opposite direction.
    1. Find the second data synchronization task, and click Configure Synchronization Channel in the Actions column.
      Configure the data synchronization task in the opposite direction
    2. Repeat substeps ii to viii that are described in step 5.

Result

Wait until both data synchronization tasks are in the Synchronizing state.Two-way data synchronization configured