Using the SqlServer module, it is possible to set up, maintain, and remove SqlAvailability groups. Creating a new SqlAvailability group can be quite complex in T-SQL; however, it is surprisingly simple in PowerShell.

First, we need to establish a connection to both the primary and the secondary instance. This speeds up subsequent calls and ensures both instances are available:

$primaryServer = Get-SqlInstance -MachineName PrimaryComputer -Name Instance
$secondaryServer = Get-SqlInstance -MachineName SecondaryComputer -Name Instance

Next, it is necessary to clone the database you want mirrored onto the replica server. For this, you can use Backup-SqlDatabase and Restore-SqlDatabase, as follows:

# Backup database and log from primary server
$paramBackupSqlDatabase = @{
    Database     = "Database1"
    BackupFile   = \fileserverackupsDatabase1.bak
    InputObject  = $primaryServer
}
Backup-SqlDatabase @paramBackupSqlDatabase

$paramBackupSqlDatabase = @{
    Database     = "Database1"
    BackupFile   = \fileserverackupsDatabase1.log
    InputObject  = $secondaryServer
    BackupAction = 'Log'
}

Backup-SqlDatabase @paramBackupSqlDatabase

# Restore the database and log on the secondary (using NO RECOVERY)  
$paramRestoreSqlDatabase = @{
    Database     = "Database1"
    BackupFile   = \fileserverackupsDatabase1.bak
    InputObject  = $secondaryServer
    NoRecovery   = $true
}
Restore-SqlDatabase @paramRestoreSqlDatabase

$paramRestoreSqlDatabase = @{
    Database      = "Database1"
    BackupFile    = \fileserverackupsDatabase1.log
    InputObject   = $secondaryServer
    RestoreAction = 'Log'
    NoRecovery    = $true
}
Restore-SqlDatabase @paramRestoreSqlDatabase

Next, we define the replication on both replica and primary in memory:

# Create an in-memory representation of the primary replica.
$paramNewSqlAvailabilityReplica = @{
    Name              = "PrimaryComputerInstance"
    EndpointUrl       = "TCP://PrimaryComputer.domain.com:5022"
    AvailabilityMode  = "SynchronousCommit"
    FailoverMode      = "Automatic"
    Version           = 12
    AsTemplate        = $true
}
$primaryReplica = New-SqlAvailabilityReplica @paramNewSqlAvailabilityReplica
 
# Create an in-memory representation of the secondary replica.  
$paramNewSqlAvailabilityReplica = @{
    Name              = "SecondaryComputerInstance"
    EndpointUrl       = "TCP://SecondaryComputer.domain.com:5022"
    AvailabilityMode  = "SynchronousCommit"
    FailoverMode      = "Automatic"
    Version           = 12
    AsTemplate        = $true
}
$secondaryReplica = New-SqlAvailabilityReplica @paramNewSqlAvailabilityReplica

Finally, we use the two replicas to define a replication group on the primary, join the secondary instance, and add its copy of the database to the availability group:

# Create the availability group
$paramNewSqlAvailabilityGroup = @{
    Name                 = "AvailabilityGroup1"
    InputObject          = $primaryServer
    AvailabilityReplica  = @($primaryReplica, $secondaryReplica)
    Database             = "Database1"
}
New-SqlAvailabilityGroup @paramNewSqlAvailabilityGroup

# Join the secondary replica to the availability group. 
$paramJoinSqlAvailabilityGroup = @{
    InputObject  = $secondaryServer
    Name         = "AvailabilityGroup1"
}
Join-SqlAvailabilityGroup @paramJoinSqlAvailabilityGroup

# Join the secondary database to the availability group.
$paramAddSqlAvailabilityDatabase = @{
    Path      = "SQLSERVER:SQLSecondaryComputerInstanceAvailabilityGroupsAvailabilityGroup1"
    Database  = "Database1"
}
Add-SqlAvailabilityDatabase @paramAddSqlAvailabilityDatabase

With that, the availability group should be up and running.