環境：
2臺SQL Server 2012 Always ON服務
現象：
Always ON服務正常，同步正常，應用正常。
Second Server Server Agent 啓動數秒後就自動停止。
處理過程：
1、查看Windows 系統日誌，顯示如下信息：
2、在SQL Studio 中查看當前Error Log
Date,Source,Severity,Message
09/25/2018 13:54:07,,Information,[098] SQLServerAgent terminated (normally)
09/25/2018 13:54:07,,Error,[382] Logon to server 'domain\SQLInstance' failed (DisableAgentXPs)
09/25/2018 13:54:07,,Error,[165] ODBC Error: 0<c/> Data source name not found and no default driver specified [SQLSTATE IM002]
09/25/2018 13:54:07,,Error,[165] ODBC Error: 0<c/> Data source name not found and no default driver specified [SQLSTATE IM002]
09/25/2018 13:54:07,,Error,[165] ODBC Error: 0<c/> Data source name not found and no default driver specified [SQLSTATE IM002]
09/25/2018 13:54:07,,Error,[165] ODBC Error: 0<c/> Data source name not found and no default driver specified [SQLSTATE IM002]
09/25/2018 13:54:07,,Error,[165] ODBC Error: 0<c/> Data source name not found and no default driver specified [SQLSTATE IM002]
09/25/2018 13:54:07,,Error,[000] Unable to connect to server 'domain\SQLInstance'; SQLServerAgent cannot start
09/25/2018 13:54:07,,Error,[150] SQL Server does not accept the connection (error: 0). Waiting for Sql Server to allow connections. Operation attempted was: Verify Connection On Start.
09/25/2018 13:53:37,,Error,[150] SQL Server does not accept the connection (error: 0). Waiting for Sql Server to allow connections. Operation attempted was: Verify Connection On Start.
09/25/2018 13:53:07,,Error,[150] SQL Server does not accept the connection (error: 0). Waiting for Sql Server to allow connections. Operation attempted was: Verify Connection On Start.
09/25/2018 13:52:37,,Error,[150] SQL Server does not accept the connection (error: 0). Waiting for Sql Server to allow connections. Operation attempted was: Verify Connection On Start.
09/25/2018 13:52:07,,Error,[150] SQL Server does not accept the connection (error: 0). Waiting for Sql Server to allow connections. Operation attempted was: Verify Connection On Start.
09/25/2018 13:52:07,,Information,[495] The SQL Server Agent startup service account is domain\dbadmin.
09/25/2018 13:52:07,,Information,[100] Microsoft SQLServerAgent version 11.0.3000.0 (X64 unicode retail build) : Process ID 1008
3、結合以上錯誤，似乎都指向ODBC，打開ODBC，發現ODBC 64bit 中Driver爲空
正常是應該有SQL Server和 SQL Native Client 11這兩個驅動的。
4、在SQL Server 2012 安裝包中找到sqlncli.msi 重新安裝SQL Native Client 11(注意選擇重裝，而不是修復)。
5、再次在ODBC中查看，SQL Native Client 11已經有了。
6、重啓SQL Agent ，觀察幾分鐘後沒有再出現自動停止的現象，問題解決。
後面有看到一篇介紹ODBC驅動丟失的文章：http://www.cnblogs.com/chinalantian/archive/2016/06/13/5581644.html
瞭解到可能是卸載某些軟件的時候會把ODBC中的部分驅動也刪除，諮詢客戶表示近期有刪除一些軟件。
特此記錄！