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AlwaysOn Availability Group Design

SQL Server 2012/2014 AlwaysOn Availability Groups:

 


This part describe the design of the environment.

Article summary: SQL Server 2012-2014 AlwaysOn Availability Group

For the tests, I will create an “AlwaysOn Availability Group” cluster with four nodes and four AAG. Each AAG has two SQL Server Instance members, so each SQL node participate to two AAG.

The first two AAG will be used to host only test Databases. The other two will be used to host databases for SCOM 2012 R2 and SCO 2012 R2.

Schema AlwaysOn Availability Groups - Design - Multiple AAG - Replication Network

Schema: AlwaysOn Availability Groups Design with multiple AAG on four Nodes and a dedicated Network for Replication

AlwaysOn Cluster – Physical View

Schema - AlwaysOn Availability Groups Physical View (DataCenter Fault Tolerance)

Schema: AlwaysOn Availability Groups Physical View (DataCenter Fault Tolerance)

 

LAB Requirements

Three Networks are required.

vSwitch Description Subnet
vSwitch0-Public Client Access 10.0.1.0 /24
vSwitch1-Cluster Heartbeat 10.0.10.0 /24
vSwitch2-Replication AAG Replication 10.0.20.0 /24

Note: I use same subnet for all nodes, I’ll write an article for WSFC Cluster Administration/Troubleshoot which also cover cross-subnet configuration.

Infra server:

Server Description IP
M-DCDNS AD Root / DNS 10.0.1.1

 

SQL Servers / Instances Configuration

The lab will be composed on a four node WSFC cluster:

 

Hostname OS IP VLAN Public IP VLAN CLUSTER IP VLAN Replication Note
M-SQLA1 WS2012R2 10.0.1.21 10.0.10.21 10.0.20.21
M-SQLA2 WS2012R2-CORE 10.0.1.22 10.0.10.22 10.0.20.22
M-SQLA3 WS2012R2-CORE 10.0.1.23 10.0.10.23 10.0.20.23
M-SQLA4 WS2012R2-CORE 10.0.1.24 10.0.10.24 10.0.20.24
clustsqlao1 n/a 10.0.1.25 n/a n/a Cluster Resource Name

M-SQLA1 OS will be installed in full GUI mode with the SQL Feature “Management Tools – Complete” (include “Management Studio”; it’s not compatible with a Core installation). This server will be used to manage SQL AAG and WSFC cluster.

Note: In a production environment, all servers must be identical (all in core mode, or full/minimal) and a dedicated “management/tools” server with consoles is used for administration.

Best Practices and Recommendations
It’s recommended to use the Windows Server Core Installation option for setting up a SQL server environment (especially if it’s virtualized).
Advantages of a SQL Core installation:
  • reduce the space required on disk.
  • reduce the potential attack surface.
  • reduce the overhead of updating patches.
  • minimize the requirements for servicing and restarting the server.

 

We need to install one named-instance per SQL Server:

Server Instance Name Instance Port SQL Features
M-SQL1 aoi1 1764 SQL Database Engine
Full-Text Search (needed for SCOM)
M-SQL2 aoi2 1764
M-SQL3 aoi3 1764
M-SQL4 aoi4 1764

 

Note Port Instances/Listener:

For an AAG Environment, you have to choice Ports for instances (here x4) and Ports for AAG-Listener (also x4 in my lab). I choose to use the same port (but not the default 1433) for all instances and all AAG Listeners, but there is no restriction. You can use different ports for each instance, different ports for each Listener, same port for all instances and another port for all Listeners, etc…

 

Availability Groups Configuration

I will create four Availability Groups:

AAG Members (Instance) Default Role AAG Listener Databases

Name

IP

Port

AAG-1 m-sqla1\aoi1 Primary AAG-1L 10.0.1.41 1764 DBTest01
m-sqla3\aoi3 Secondary
AAG-2 m-sqla1\aoi1 Secondary AAG-2L 10.0.1.42 1764 DBTest02
m-sqla3\aoi3 Primary
AAG-3SCOM m-sqla2\aoi2 Primary AAG-3L 10.0.1.43 1764 SCOM OP
m-sqla4\aoi4 Secondary
AAG-4SCOM m-sqla2\aoi2 Secondary AAG-4L 10.0.1.44 1764 SCOM DW
DB Orchestrator
m-sqla4\aoi4 Primary

AAG-1 and AAG-2 will serve for tests only. AAG-3SCOM and AAG-4SCOM will be used for my SCOM and Orchestrator Labs.

In this configuration, in nominal mode each instance hosts an “Active” Primary Replica.

The simulation is m-sql1 and m-sql2 in the same room and the two others in another room.

So I can lose one room (all my AAG/Databases remain available)

 

AAG Listener (VNN – Virtual Network Name)

For reminder, on the WSFC cluster side an AAG is a cluster Resource Group and the VNN is two cluster resources:

  • Virtual Name
  • Virtual IP

Example:


When you configure an application to host its Database on a SQL Availability Group you have to specify the Listener name for the instance name and the Listener port for the Instance port.

 

AAG Implementation – Version 1

This is the first version that will be configured in the next parts of the article:

 

Schema AlwaysOn Availabilty Groups Design 4 AAG v1

Schema: Design 4x AlwaysOn Availability Groups with Synchronous Replicas – V1

AAG Implementation – Version 2

In another part, to simulate a Remote DRP Site, I will add and additional Instance (with two Replicas in Asynchronous mode on the AAG-1 and the AAG-2):

 

Schema AlwaysOn Availability Groups Design 4 AAG v2

Schema: Design 4x AlwaysOn Availability Groups with Synchronous/Asynchronous Replicas – V2

Availability Replicas Configuration

The next part is to specify the detailed availability replica (two per AAG) configuration:

AAG Server Instance Initial Role Automatic
Failover
Synchronous
Commit
Allow Readable
Secondary
AAG-1 m-sqla1\AOI1 Primary Yes Yes Yes
m-sqla3\AOI3 Secondary Yes Yes Yes
AAG-2 m-sqla1\AOI1 Secondary Yes Yes Yes
m-sqla3\AOI3 Primary Yes Yes Yes
AAG-3SCOM m-sqla2\AOI2 Primary Yes Yes Yes
m-sqla4\AOI4 Secondary Yes Yes Yes
AAG-4SCOM m-sqla2\AOI2 Secondary Yes Yes Yes
m-sqla4\AOI4 Primary Yes Yes Yes

All replicas will be configured in “Automatic” failover mode and so in “Synchronous” availability mode.

For more information see TechNet: Failover and Failover Modes (AlwaysOn Availability Groups) – http://technet.microsoft.com/en-us/library/hh213151

 

Readable Secondary Option:

For future tests, I enable Readable Secondary option.

Option Description
No No user connections are allowed to secondary databases of this replica. They are not available for read access. This is the default setting.
Read-intent only Only read-only connections are allowed to secondary databases of this replica. The secondary database(s) are all available for read access.
Yes All connections are allowed to secondary databases of this replica, but only for read access. The secondary database(s) are all available for read access.

 

Primary Role Connections:

I use the default settings (Allow all connections).

Option Description
Allow all connections All connections are allowed to the databases in the primary replica. This is the default setting.
Allow read/write connections When the Application Intent property is set to ReadWrite or the Application Intent connection property is not set, the connection is allowed. Connections where the Application Intent connection property is set to ReadOnly are not allowed. This can help prevent customers from connecting a read-intent work load to the primary replica by mistake.

 

Endpoints Configuration

There is one Endpoint per SQL Server Instance.

During AAG Creation (via Wizard), Endpoint URL is configured with the SQL Instance FQDN. With this default option, instances will communicate over the Public Network (for reminder: 10.0.1.0/24).

So to configured instance communication on the Replication Network (10.0.20.0/24) I have to set my endpoint to: TCP://10.0.20.x:5022.

For tests, I will configure two instances (AOI1 and AOI3) on the Public Network (with FQDN) and the two other instances (AOI2 and AOI4) on the Replication Network.

Server Instance Endpoint URL Endpoint Port Endpoint Name
m-sqla1\AOI1 TCP://M-SQLA1.lab1.ad:5022 5022 Hadr_endpoint
m-sqla2\AOI2 TCP://10.0.20.22:5022 5022 Hadr_endpoint
m-sqla3\AOI3 TCP://M-SQLA3.lab1.ad:5022 5022 Hadr_endpoint
m-sqla4\AOI4 TCP://10.0.20.24:5022 5022 Hadr_endpoint

 

Note: 5022 is the default port, you can use another port.

 

Service Accounts Requirement

Isolate Instance Services

Isolating services reduces the risk that one compromised service could be used to compromise others.

At the Instance level, each SQL Service (SQL Server, SQL Agent …) must be configured with different account.

Isolate Instances

A Security Best Practice is to use different accounts for each instance, but considers these points:

  • Microsoft recommends to use the same account for all instances of an AlwaysOn Cluster (it’s more simple to assign rights to Endpoints)
  • If you want to use Kerberos, instances must use the same account:

     

Service Accounts – Solutions

Use the same account for all Instances (enable Kerberos authentication):

  • gMSA (Group Managed Service Accounts): the best solution for the AlwaysOn Availability Group is to use a gMSA (same as a MSA account but available on multiple host). But it’s not supported for the moment on SQL Server…

 

Status about  gMSA/MSA accounts for SQL

http://blogs.msdn.com/b/sqlosteam/archive/2014/02/19/msa-accounts-used-with-sql.aspx

Group Managed Service Accounts Overview

http://technet.microsoft.com/en-us/library/hh831782.aspx

 

  • “Classic” Domain Account:
    you can use the same domain account for all instances (this works), but when you have to change the password account you have to program an interruption of service (all node will be affected at the same time by the password change…)

 

Use different accounts for all Instances (disable Kerberos authentication):

    • MSA (Managed Service Account): you can use a MSA account per Instance (MSA is a domain account; password is managed automatically by the domain controller; a MSA is assigned to only one host)

 

  • Virtual Accounts: you can use a virtual account per Instance (the functioning is identical to a MSA except it’s a local account managed by the host, not by the DC). This is the default option during a SQL Instance installation.

 

For more information, see TechNet article: Configure Windows Service Accounts and Permissions – http://msdn.microsoft.com/en-us/library/ms143504.aspx

So actually, there is no possible solution for use Kerberos with AAG in a production environment. I will use MSA account for my lab.

Account MSA Description Member Of / Rights Instance Service Mode
lab1\SQLAlwaysOnAdmins n/a SQL Administrators Group Local Administrator of all nodes
Sysadmin on all instance
n/a n/a
lab1\sqlaoinstall No Account use for Installation Member of SQLAOAdmins Group n/a n/a
lab1\svc-sqldbe1 Yes SQL Service – Database Engine Domain User aoi1 Automatic
lab1\svc-sqlagt1 Yes SQL Service – Agent Domain User Automatic
lab1\svc-sqldbe2 Yes SQL Service – Database Engine Domain User aoi2 Automatic
lab1\svc-sqlagt2 Yes SQL Service – Agent Domain User Automatic
lab1\svc-sqldbe3 Yes SQL Service – Database Engine Domain User aoi3 Automatic
lab1\svc-sqlagt3 Yes SQL Service – Agent Domain User Automatic
lab1\svc-sqldbe4 Yes SQL Service – Database Engine Domain User aoi4 Automatic
lab1\svc-sqlagt4 Yes SQL Service – Agent Domain User Automatic

 

Permission needed for Service Account:

Notes: During installation, these permissions are granted by the SQL setup.

Service Description Permissions granted by SQL Server Setup
SQL Server Database Services The service for the SQL Server relational Database Engine. The executable file is <MSSQLPATH>\MSSQL\Binn\sqlservr.exe. Log on as a service
Replace a process-level token
Bypass traverse checking
Adjust memory quotas for a process
Permission to start SQL Writer
Permission to read the Event Log service
Permission to read the Remote Procedure Call service
SQL Server Agent Executes jobs, monitors SQL Server, fires alerts, and enables automation of some administrative tasks. The executable file is <MSSQLPATH>\MSSQL\Binn\sqlagent.exe. Log on as a service
Replace a process-level token
Bypass traverse checking
Adjust memory quotas for a process
Reporting Services Manages, executes, creates, schedules, and delivers reports. The executable file is <MSSQLPATH>\Reporting Services\ReportServer\Bin\ReportingServicesService.exe. Log on as a service
SQL Server Browser The name resolution service that provides SQL Server connection information for client computers. The executable path is c:\Program Files (x86)\Microsoft SQL Server\90\Shared\sqlbrowser.exe Log on as a service
Full-text search Quickly creates full-text indexes on content and properties of structured and semistructured data to provide document filtering and word-breaking for SQL Server. Log on as a service
Adjust memory quotas for a process
Bypass traverse checking

 

Storage

Disk configuration per node:

Disk Letter RAID Level Size Name SQL Path Description
disk0 c: n/a 25GB System C:\Program Files\Microsoft SQL Server\
C:\Program Files (x86) \Microsoft SQL Server\
C:\MSSQL\MSSQL11.<instancename>\
C:\MSSQL\MSSQL11.<instancename>\MSSQL\Data
SQL Shared Features
SQL Shared Features
SQL Server Directory
System Databases
disk1 G: n/a 5 GB SQL_DB G:\MSSQL\AOREPLICA\Data
G:\MSSQL\MSSQL11.<instancename>\MSSQL\TempDB\Data
G:\MSSQL\MSSQL11.<instancename>\MSSQL\Backup
Databases
TempDB Database
Database Backups
disk2 L: n/a 5 GB SQL_LOG L:\MSSQL\AOREPLICA\Log
L:\MSSQL\MSSQL11.<instancename>\MSSQL\TempDB\Log
DB Transaction Log
TempDB Log

 

Notes about Storage:

If your SQL Servers are virtualized, for production environment you shouldn’t use Virtual Disk (except for OS). You have to use Pass-through (via Virtual FC) for Hyper-V, or RDM LUN for VMware.

In addition for better performance you must use a dedicated disk for TempDB.

Install SQL Server (SQL Server Directory) on a separate disk (D:).

You can also add a separate disk for pagefile, but if the SQL server is correctly sized it should not have to swap.

 

Example of a Production configuration

Disk Letter RAID Level Size Name SQL Path Description
disk0 C: Raid 1 xx GB System C:\Program Files\Microsoft SQL Server\
C:\Program Files (x86) \Microsoft SQL Server\
SQL Shared Features
SQL Shared Features
disk1 D: Raid 1 xx GB SQL_BIN D:\MSSQL\MSSQL11.<instancename>\
D:\MSSQL\MSSQL11.<instancename>\MSSQL\Data
SQL Server Directory
System Databases
disk2 G: Raid 10 xx GB SQL_DB G:\MSSQL\AOREPLICA\Data Databases
disk3 K: Raid 5 xx GB SQL_BAK K:\MSSQL\MSSQL11.<instancename>\MSSQL\Backup Database Backups
disk4 L: Raid 10 xx GB SQL_LOG L:\MSSQL\AOREPLICA\Log Transaction Log
disk5 T: Raid 10 xx GB SQL_TEMPDB T:\MSSQL\MSSQL11.<instancename>\MSSQL\TempDB\Data
T:\MSSQL\MSSQL11.<instancename>\MSSQL\TempDB\Log
TempDB Database
TempDB Logs
disk6 R: Raid 5 xx GB SQL_SSRS R:\MSSQL\MSSQL11.<instancename>\MSSQL\Reports SSRS Feature

 

Note for Databases/Logs path on AAG:

If you use the default instance path (which contains the instance name) for Databases and Logs, the paths on all the nodes participating to the AAG are different. This has an impact on AlwaysOn AG.

TechNet:

If the file path (including the drive letter) of a secondary database differs from the path of the corresponding primary database, the following restrictions apply:

  • New Availability Group Wizard/Add Database to Availability Group Wizard:  The Full option is not supported (on the “Select Initial Data Synchronization” Page).
  • RESTORE WITH MOVE:  To create the secondary databases, the database files must be RESTORED WITH MOVE on each instance of SQL Server that hosts a secondary replica.
  • Impact on add-file operations:  A later add-file operation on the primary replica might fail on the secondary databases. This failure could cause the secondary databases to be suspended. This, in turn, causes the secondary replicas to enter the NOT SYNCHRONIZING state.

 

So it is recommended to use the same path on all instances:

Data Default Path New Path
DB G:\MSSQL\MSSQL11.<instancename>\MSSQL\Data G:\MSSQL\AOREPLICA\Data
LOG L:\MSSQL\MSSQL11.<instancename>\MSSQL\Log L:\MSSQL\AOREPLICA\Log

 

Note about TempDB

  • The TempDB shouldn’t be store on the same disk as your Databases
  • In Production, autogrow operations can affect performance so preallocate space to allow for the expected workload (autogrow should be used to increase disk space for unplanned exceptions)
  • SQL CAT team recommends one file per CPU Core. Microsoft Note:

But this recommendation is subject to discussion and depends of your SQL environment (and the TempDB Contention). I’m not going to analyze this in this article, but I invite you to read the great articles of Paul Randal:

A SQL Server DBA myth a day: (12/30) tempdb should always have one data file per processor core:
http://www.sqlskills.com/blogs/paul/a-sql-server-dba-myth-a-day-1230-tempdb-should-always-have-one-data-file-per-processor-core/

The Accidental DBA (Day 27 of 30): Troubleshooting: Tempdb Contention: http://www.sqlskills.com/blogs/paul/the-accidental-dba-day-27-of-30-troubleshooting-tempdb-contention/

Another “General” Recommendation:

Last year at PASS 2011 Bob Ward, one the Sr Escalation Engineers for SQL, made the following recommendation which will be updated in the Microsoft references that other people provided on this thread:

As a general rule, if the number of logical processors is less than 8, use the same number of data files as logical processors. If the number of logical processors is greater than 8, use 8 data files and then if contention continues, increase the number of data files by multiples of 4 (up to the number of logical processors) until the contention is reduced to acceptable levels or make changes to the workload/code.

http://social.msdn.microsoft.com/Forums/sqlserver/en-US/dceea24c-7a53-4450-94cd-8327b5daa759/what-is-the-best-practice-for-configuring-tempdb

 

Security

Firewall

These ports (incoming) must be opened:

Service Protocol Port Name Managed by
Windows (*)
Note
SQL TCP 1764 Instance and VNN Port    
SQL TCP 5022 Instance SQL Endpoint   User for AAG Replica Communication
WSFC Cluster TCP 3343 Failover Clusters (TCP-In) Yes Required during a node join operation
WSFC Cluster UDP 3343 Failover Clusters (UDP-In) Yes  
WSFC Cluster TCP 135 Failover Clusters (DCOM-RPC-EPMAP-In) Yes  
WSFC Cluster TCP 445 Failover Clusters – Named Pipes (NP-In) Yes  
WSFC Cluster TCP <Dynamic> Failover Clusters <RPC Server Programs> Yes  
(*) Rules are automatically created during the feature/role installation

For more information about Microsoft Products Port requirements see MS KB “Service overview and network port requirements for Windows” – http://support.microsoft.com/kb/832017/en-us#method70

 

Antivirus Exclusion

Configure these exclusions on your Antivirus:

Exclusions for Cluster:

Type Detail (Path, Extension,…) Description
Folder %Systemroot%\Cluster Cluster folder
Folder Q:\mscs Qurom disk

Exclusions for SQL Server:

Type Detail (Path, Extension,…) Description
File-name extensions .mdf
.ldf
.ndf
SQL Server data files
Process <installpath>\MSSQL11.<Instance Name>\MSSQL\Binn\SQLServr.exe SQL process

 

Next

Next par covers the installation and configuration of servers in core mode: AlwaysOn Availability Group – Part 3 – Install WS2012 R2 Core Server

 

About Gilles Monville

Gilles Monville is a passionate of IT for many years; he works for over 10 years on Microsoft and VMware environments. In addition to Virtualization and Cloud computing, he loves automation (Orchestrator, PowerShell, Cloud deployment …)

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