SQL Server Replication provides multi-faceted data movement capabilities across SQL Server releases which has been used by customers across the globe for a large number of years. When moving from one major release of SQL Server to another, replication topology upgrade has been a constant topic of lengthy discussions. In this post, we shall outline some of the challenges of upgrading SQL Server replication environments to SQL Server 2016. The requirements of upgrading a replication topology need to abide by the following guidelines:
- A Distributor can be any version as long as it is greater than or equal to the Publisher version (in many cases the Distributor is the same instance as the Publisher).
- A Publisher can be any version as long as it less than or equal to the Distributor version.
-
Subscriber version depends on the type of publication:
- A Subscriber to a transactional publication can be any version within two versions (n-2) of the Publisher version. For example: a SQL Server 2012 Publisher can have SQL Server 2014 and SQL Server 2016 Subscribers; and a SQL Server 2016 Publisher can have SQL Server 2014 and SQL Server 2012 Subscribers.
- A Subscriber to a merge publication can be any version less than or equal to the Publisher version.
If you had to draw a support matrix for the major release versions for transactional and merge replication, the output would be the two tables shown below.
Transactional Replication Matrix
| Publisher | Distributor | Subscriber |
| SQL Server 2016 | SQL Server 2016 |
SQL Server 2016
SQL Server 2014 SQL Server 2012 |
| SQL Server 2014 |
SQL Server 2016
SQL Server 2014 |
SQL Server 2016
SQL Server 2014 SQL Server 2012 SQL Server 2008 R2 SQL Server 2008 |
| SQL Server 2012 |
SQL Server 2016
SQL Server 2014 SQL Server 2012
|
SQL Server 2016
SQL Server 2014 SQL Server 2012 SQL Server 2008 R2 SQL Server 2008 |
|
SQL Server 2008 R2
SQL Server 2008 |
SQL Server 2016
SQL Server 2014 SQL Server 2012 SQL Server 2008 R2 SQL Server 2008 |
SQL Server 2014
SQL Server 2012 SQL Server 2008 R2 SQL Server 2008 SQL Server 2005 SQL Server 2000 |
Merge Replication Support Matrix
| Publisher | Distributor | Subscriber |
| SQL Server 2016 | SQL Server 2016 |
SQL Server 2016
SQL Server 2014 SQL Server 2012 |
| SQL Server 2014 |
SQL Server 2016
SQL Server 2014 |
SQL Server 2014
SQL Server 2012 SQL Server 2008 R2 SQL Server 2008 |
| SQL Server 2012 | SQL Server 2012 |
SQL Server 2012
SQL Server 2008 R2 SQL Server 2008 |
|
SQL Server 2008
SQL Server 2008 R2 |
SQL Server 2008 R2
SQL Server 2008 |
SQL Server 2008 R2
SQL Server 2008 SQL Server 2005 SQL Server 2000 |
If you notice the line items for SQL Server 2016, you will see that a topology is unable to support SQL Server 2016 in a number of scenarios when you are running SQL Server 2016 as a publisher. Replication topologies have three common deployment patterns as shown in the visio diagram below. The distributor could be on the publisher or subscriber or a remote distributor. We do come across different deployments of the publisher and subscriber which are a mix of standalone instances, SQL Server failover cluster instances or Always On Availability Group replica instances.
Depending on the deployment pattern, the upgrade path to SQL Server 2016 would be different. Let us explore the different possibilities. SQL Server offers two upgrade paths in general:
- Side-by-side: This approach involves setting up a new parallel environment and moving the databases along with the associated instance level objects like logins, jobs etc. to the new environment.
- In-place upgrade: With this approach, the SQL Server setup program upgrades the existing SQL Server installation by replacing the existing SQL Server bits with the SQL Server 2016 bits and then upgrades each of the system and user databases. For environments running SQL Server failover cluster instances or Always On Availability Groups, an in-place upgrade is combined with a rolling upgrade to minimize downtime.
The scenarios below apply to Transactional Replication (without P2P Replication, Queued Updating Subscription and Immediate Updating Subscription) and Merge Replication. The options below outline how a phased approach can be adopted for your replication topology upgrade so that you don't have to upgrade all the SQL Server instances in one big upgrade operation.
A common approach that has been adopted for side-by-side upgrades of replication topologies is to move publisher-subscriber pairs in parts to the new side-by-side environment as opposed to a movement of the entire topology. This phased approach helps to control downtime and minimize the impact to a certain extent for the businesses dependent on replication.
Upgrading a Replication Topology with a Remote Distributor
|
Transactional Replication |
|
|
|
Upgrading from |
Distributor |
Publisher/Subscriber |
|
SQL Server 2014 SQL Server 2012 |
Step 1: In-place upgrade (Can be upgraded due to n-2 support) OR Side-by-side upgrade requires re-setup of all the publisher/subscriber pairs in the replication topology* |
Step 2 : In-place upgrade (Can be upgraded due to n-2 support) OR Side-by-side upgrade of subscriber requires reinitialization of subscriber Side-by-side upgrade of publisher requires reconfiguring all the publisher-subscriber pairs The publisher and subscriber can be upgraded in any order
|
|
SQL Server 2008 R2 SQL Server 2008 |
Step 1: In-place upgrade OR Side-by-side upgrade requires re-setup of all the publisher/subscriber pairs in the replication topology* |
Step 2 : In-place upgrade would need to occur for both publisher and subscriber at the same time as publisher and subscriber need to be within two major releases. A SQL Server 2008/R2 publisher/subscriber cannot have a SQL Server 2016 publisher/subscriber. OR Intermediate In-place upgrade to SQL Server 2012/2014 of publisher or subscriber The other server in the publisher/subscriber pair can then be upgraded to SQL Server 2016 OR Side-by-side upgrade will require the upgrade of publisher and subscriber to happen together and requires a re-setup of the publisher/subscriber pairs
|
*See " Side-by-side Upgrade of the Distributor without re-initialization " below
|
Merge Replication |
|
|
|
|
Upgrading from |
Distributor |
Publisher |
Subscriber |
|
SQL Server 2014 SQL Server 2016 |
Step 1: In-place upgrade OR Side-by-side upgrade requires re-setup of all the publisher/subscriber pairs in the replication topology*
|
Step 2 : In-place upgrade OR Side-by-side upgrade of publisher requires reconfiguring all the publisher-subscriber pairs
|
Step 3 : In-place upgrade OR Side-by-side upgrade of subscriber requires reinitialization of subscriber
|
|
SQL Server 2008 R2 SQL Server 2008 |
Step 1: In-place upgrade OR Side-by-side upgrade requires re-setup of all the publisher/subscriber pairs in the replication topology* |
Step 2 : In-place upgrade OR Side-by-side upgrade of publisher requires reconfiguring all the publisher-subscriber pairs. Needs to happen with the upgrade of the subscriber. |
Step 3 : In-place upgrade OR Side-by-side upgrade of subscriber requires reinitialization of subscriber. Needs to happen with the upgrade of the publisher. |
*See " Side-by-side Upgrade of the Distributor without re-initialization " below
Upgrading a Replication Topology with Publisher acting as the Distributor
|
Transactional Replication |
|
|
|
Upgrading from |
Publisher/Distributor |
Subscriber |
|
SQL Server 2014 SQL Server 2012 |
Step 1: In-place upgrade (Can be upgraded due to n-2 support) OR Side-by-side upgrade requires re-setup of all the publisher/subscriber pairs in the replication topology* |
Step 2 : In-place upgrade (Can be upgraded due to n-2 support) OR Side-by-side upgrade of subscriber requires reinitialization of subscriber
|
|
SQL Server 2008 R2 SQL Server 2008 |
Step 1: In-place upgrade (Requires subscriber to be upgraded because publisher and subscriber need to be within two major releases. A SQL Server 2016 publisher cannot have a SQL Server 2008/R2 subscriber.) OR Intermediate in-place upgrade to SQL Server 2012/2014 for the publisher which is acting as the distributor also The subscriber can be upgrade to SQL Server 2016 post the intermediate publisher upgrade OR Side-by-side upgrade requires re-setup of all the publisher/subscriber pairs served by this distributor in the replication topology. Needs to happen with the upgrade of the subscriber. |
Step 2 : In-place upgrade would need to occur for both publisher and subscriber at the same time as publisher and subscriber need to be within two major releases. A SQL Server 2008/R2 publisher/subscriber cannot have a SQL Server 2016 publisher/subscriber. OR Intermediate In-place upgrade to SQL Server 2012/2014 of the publisher The subscriber can then be upgraded to SQL Server 2016 OR Side-by-side upgrade will require the upgrade of subscriber to happen together with the publisher and requires a re-initialization of the subscribers. Needs to happen with the upgrade of the publisher.
|
*See " Side-by-side Upgrade of the Distributor without re-initialization " below
|
Merge Replication |
|
|
|
Upgrading from |
Publisher/Distributor |
Subscriber |
|
SQL Server 2014 SQL Server 2016 |
Step 1: In-place upgrade OR Side-by-side upgrade requires re-setup of all the publisher/subscriber pairs served by this distributor in the replication topology*
|
Step 2 : In-place upgrade OR Side-by-side upgrade of subscriber requires reinitialization of subscriber
|
|
SQL Server 2008 R2 SQL Server 2008 |
Step 1: In-place upgrade OR Side-by-side upgrade requires re-setup of all the publisher/subscriber pairs served by this distributor in the replication topology. Needs to happen with the upgrade of the subscriber. |
Step 2: In-place upgrade OR Side-by-side upgrade requires re-setup of all the publisher/subscriber pairs in the replication topology. Needs to happen with the upgrade of the publisher. |
*See " Side-by-side Upgrade of the Distributor without re-initialization " below
Upgrading a Replication Topology with Subscriber acting as the Distributor
|
Transactional Replication |
|
|
|
Upgrading from |
Distributor/Subscriber |
Publisher |
|
SQL Server 2014 SQL Server 2012 |
Step 1: In-place upgrade (Can be upgraded due to n-2 support) OR Side-by-side upgrade requires re-setup of publisher/subscriber pairs in the replication topology served by this distributor* |
Step 2 : In-place upgrade (Can be upgraded due to n-2 support) OR Side-by-side upgrade of subscriber requires re-setup of all the publisher/subscriber pairs
|
|
SQL Server 2008 R2 SQL Server 2008 |
Step 1: In-place upgrade (Requires publisher to be upgraded also because subscriber and publisher need to be within two major releases. A SQL Server 2008/R2 publisher cannot have a SQL Server 2016 subscriber.) OR Intermediate in-place upgrade to SQL Server 2012/2014 for the subscriber which is acting as the distributor also The publisher can then be upgraded to SQL Server 2016 post this intermediate distributor upgrade OR Side-by-side upgrade of distributor/subscriber requires re-setup of all the publisher/subscriber pairs served by this distributor. Needs to happen with the upgrade of the publisher.
|
Step 2 : In-place upgrade would need to occur for both publisher and subscriber at the same time as publisher and subscriber need to be within two major releases. A SQL Server 2008/R2 publisher/subscriber cannot have a SQL Server 2016 publisher/subscriber. OR The publisher can then be upgraded to SQL Server 2016 (Requires intermediate In-place upgrade to SQL Server 2012/2014 of the subscriber) OR Side-by-side upgrade requires re-setup of all the publisher/subscriber pairs in the replication topology. Needs to happen with the upgrade of the distributor/subscriber.
|
*See " Side-by-side Upgrade of the Distributor without re-initialization " below
|
Merge Replication |
|
|
|
Upgrading from |
Distributor/Subscriber |
Publisher |
|
SQL Server 2014 SQL Server 2016 |
Step 1: In-place upgrade OR Side-by-side upgrade requires re-setup of all the publisher/subscriber pairs in the replication topology served by this distributor*. This also requires upgrade of the publisher as the publisher version has to be higher than the subscriber.
|
Step 2 : In-place upgrade OR Side-by-side upgrade of subscriber requires reinitialization of all publisher/subscriber pairs. Requires simultaneous upgrade of the subscriber because it is acting as the distributor.
|
|
SQL Server 2008 R2 SQL Server 2008 |
Step 1: In-place upgrade (Requires simultaneous upgrade of the publisher) OR Side-by-side upgrade requires re-setup of all the publisher/subscriber pairs in the replication topology. Requires simultaneous upgrade of the publisher. |
Step 2: In-place upgrade (Requires simultaneous upgrade of the subscriber acting as the distributor) OR Side-by-side upgrade requires re-setup of all the publisher/subscriber pairs in the replication topology. Requires simultaneous upgrade of the subscriber because it is acting as the distributor. |
*See " Side-by-side Upgrade of the Distributor without re-initialization " below
Side-by-side Upgrade of the Distributor without re-initialization
If you are running your SQL Server instance to be upgraded on Windows Server 2008 or Windows Server 2008 R2, then you will need to perform a side-by-side upgrade of the distributor first to Windows Server 2012 R2 or Windows Server 2016 before upgrading to SQL Server 2016. The reason for this intermediate OS upgrade is that SQL Server 2016 cannot be installed on a Windows Server 2008/2008 R2 server. The side-by-side approach can also help reduce downtime if you are upgrading the hardware of the Windows Server hosting the distributor instance. Downtime of the publisher and subscriber can be reduced using SQL Server Failover Cluster instances or Always On Availability Groups.
The assumption here is that the edition of the SQL Server instance will not change and a failover cluster instance of SQL Server will be upgraded to a failover cluster instance where as a standalone instance will be upgraded to a standalone instance using the steps mentioned below.
Steps for side-by-side migration of the distributor to Windows Server 2012 R2
- Setup a new failover cluster or standalone instance running the same major release, edition and version as your distributor on Windows Server 2012 R2/2016 with a different windows cluster and SQL Server FCI name or standalone host name. You will need to keep the directory structure same as the old distributor to ensure that the replication agents executables, replication folders and database file paths are found at the same path on the new environment. This will reduce any post migration/upgrade steps required.
- Make sure that the current synchronization is complete and post that shut down all the replication agents
- Shut down the current SQL Server failover cluster instance or standalone instance running as the distributor. If this is a standalone instance of SQL Server, you will need to shutdown the Windows Server hosting the SQL Server instance to ensure that there is no conflict while renaming the server.
- Remove the DNS entries for the old (current distributor instance) environment and the AD entries for the computer object for the SQL Server FCI
- If this is a SQL Server Failover Cluster instance, rename the new SQL Server Failover Cluster instance name with the old virtual server name. If this is a standalone SQL Server instance, then rename the new standalone host with the old hostname.
- Copy the database files from the previous instance using SAN redirection or storage copy or file copy
- Bring the new SQL Server instance online
- Restart all the replication agents and verify if the agents are running successfully
- Validate if replication is working as expected
In-place upgrade to SQL Server 2016
- Run in-place upgrade for SQL Server 2016 on the new cluster
- If required, rebuild old nodes and add to the cluster to re-use existing hardware
- Validate if replication is working fine
If you want to reduce the downtime, we recommend that you perform the side-by-side migration of the distributor as one activity and the in-place upgrade to SQL Server 2016 as another activity. This will allow you to take a phased approach, reduce risk and minimize downtime.
Summary
Upgrading a replication topology is a multi-step process. We recommend attempting an upgrade of a replica of your replication topology in a test environment before running the upgrade on the actual production environment. This will help iron out any operational documentation that is required for handling the upgrade smoothly without incurring expensive and long downtimes during the actual upgrade process. We have seen customers reduce downtime significantly with the use of Always On Availability Groups and/or SQL Server Failover Cluster Instances for their production environments while upgrading their replication topology. Additionally, we recommend taking backups of all the databases including MSDB, Master, Distribution database(s) and the user databases participating in replication before attempting the upgrade.
Resources
Recovering a Deleted Cluster Name Object (CNO) in a Windows Server 2008 Failover Cluster
Upgrade Replicated Databases
Supported Version and Edition Upgrades for SQL Server 2016
Hardware and Software Requirements for SQL Server 2016
SQL Server Upgrade
Rename a Computer that hosts a Standalone instance of SQL Server
Rename a SQL Server Virtual Server Name
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