How to check history of primary node in an Availability Group?

Here's my go-to query to pull the events that Aaron mentioned (availability_replica_state_change). This script also takes the liberty of converting the UTC time to your local time:

declare @xel_path varchar(1024);
declare @utc_adjustment int = datediff(hour, getutcdate(), getdate());

-------------------------------------------------------------------------------
------------------- target event_file path retrieval --------------------------
-------------------------------------------------------------------------------
;with target_data_cte as
(
    select  
        target_data = 
            convert(xml, target_data)
    from sys.dm_xe_sessions s
    inner join sys.dm_xe_session_targets st
    on s.address = st.event_session_address
    where s.name = 'alwayson_health'
    and st.target_name = 'event_file'
),
full_path_cte as
(
    select
        full_path = 
            target_data.value('(EventFileTarget/File/@name)[1]', 'varchar(1024)')
    from target_data_cte
)
select
    @xel_path = 
        left(full_path, len(full_path) - charindex('\', reverse(full_path))) + 
        '\AlwaysOn_health*.xel'
from full_path_cte;

-------------------------------------------------------------------------------
------------------- replica state change events -------------------------------
-------------------------------------------------------------------------------
;with state_change_data as
(
    select
        object_name,
        event_data = 
            convert(xml, event_data)
    from sys.fn_xe_file_target_read_file(@xel_path, null, null, null)
)
select
    object_name,
    event_timestamp = 
        dateadd(hour, @utc_adjustment, event_data.value('(event/@timestamp)[1]', 'datetime')),
    ag_name = 
        event_data.value('(event/data[@name = "availability_group_name"]/value)[1]', 'varchar(64)'),
    previous_state = 
        event_data.value('(event/data[@name = "previous_state"]/text)[1]', 'varchar(64)'),
    current_state = 
        event_data.value('(event/data[@name = "current_state"]/text)[1]', 'varchar(64)')
from state_change_data
where object_name = 'availability_replica_state_change'
order by event_timestamp desc;

Look for availability_replica_state_change events in the AlwaysOn_health extended events session. If this session is not running:

ALTER EVENT SESSION AlwaysOn_health ON SERVER WITH (STARTUP_STATE = ON);
ALTER EVENT SESSION AlwaysOn_health ON SERVER STATE = START;

More info:

• New AlwaysOn_health Extended Events Session in SQL Server 2012 RC0

• Answering Questions with the AlwaysOn Dashboard

• Monitoring Availability Groups Part 3 – Extended Events

• AlwaysOn Extended Events

I used the following query that I got from EXCHANGE SPILL, but slightly modified it to convert time from UTC to local.

DECLARE @FileName NVARCHAR(4000)
SELECT @FileName = target_data.value('(EventFileTarget/File/@name)[1]', 'nvarchar(4000)')
    FROM (
           SELECT CAST(target_data AS XML) target_data
            FROM sys.dm_xe_sessions s
            JOIN sys.dm_xe_session_targets t
                ON s.address = t.event_session_address
            WHERE s.name = N'AlwaysOn_health'
         ) ft;

WITH    base
          AS (
               SELECT XEData.value('(event/@timestamp)[1]', 'datetime2(3)') AS event_timestamp
                   ,XEData.value('(event/data/text)[1]', 'VARCHAR(255)') AS previous_state
                   ,XEData.value('(event/data/text)[2]', 'VARCHAR(255)') AS current_state
                   ,ar.replica_server_name
                FROM (
                       SELECT CAST(event_data AS XML) XEData
                           ,*
                        FROM sys.fn_xe_file_target_read_file(@FileName, NULL, NULL, NULL)
                        WHERE object_name = 'availability_replica_state_change'
                     ) event_data
                JOIN sys.availability_replicas ar
                    ON ar.replica_id = XEData.value('(event/data/value)[5]', 'VARCHAR(255)')
             )
    SELECT DATEADD(HOUR, DATEDIFF(HOUR, GETUTCDATE(), GETDATE()), event_timestamp) AS event_timestamp
           ,previous_state
           ,current_state
           ,replica_server_name
        FROM base
        ORDER BY event_timestamp DESC;