Exchange failover

There are two concept for DAG, Active/Passive and Active/Active. Which one you are planning?

your internet sites as primary or secondary really dont have anything to do with your DAG. As long as your exchange servers and DBs can communicate with each other it doesn't matter which site is primary or secondary internet sites. your DAG doesnt care so you can decide what works best for your environment in that regard, but that really has nothing to do with DAG.

We are active passive. What i want to understand is how do I accomplish this? What are the DNS considerations I want all mail to go thru one site unless it "goes down" or has to be taken offline. It seems simple enough to do in DNS, am I missing something?

whatever site the active DBs are in that is the site the mail will go out of and if you have a failure and passive DBs will become active and the mail will go through that site. now inbound mail is a different story and there you will either need to have 2 MX records so if 1 cant be contacted the other will accept the mail or you will need to manually switch the MX to the other site.

Thanks for sharing the information. In Active/Passive design, your passive site is in offline state. With healthy db copies. Now there are several scenario for failover and according to situation you need to take necessary steps for failover to DR site. Finally, it depends on your company RTO and RPO, how long you can afford an outage in your org. Here is a tool, which can help you to perform failovers in DR situation.
https://blogs.technet.microsoft.com/exchange/2012/10/19/exchange-2010-datacenter-switchover-tool-now-available/

Hope that helps.

I am going to put together a sanitized version of my network diagram (load balancer and spam filters) for further discussion. I will get back to you in a day or so.

This is a better diagram we are in an active passive scenario.
DAG-failover.vsdx

Thanks, let me review it. Also, tell me, what exactly you are looking here. like do you want to know, how to perform DR or anything else. Tell me your end goal.
I advise you to read these KB's:
https://docs.microsoft.com/en-us/exchange/high-availability/plan-ha?view=exchserver-2019
https://docs.microsoft.com/en-us/exchange/high-availability/deploy-ha?view=exchserver-2019

First I'd like to know if I can have site B as a primary site load balanced with site A. I would also like Site A to be a failover preferably without intervention but if necessary operator intervention.

We are presently load balanced between the two site with site a having internet access (site B does not). If we lose internet access we swing over to the cloud (message one), before you say anything, I inherited this. I feel a basic design that I am asking you to critique is a better way to go. Get rid of message one

Let me try to help you out here. First in Active/Passive design, you will have only one Site active or internet or user facing site. DR site is kind of offline site. Where your Exchange will be in passive state. When you have any issue in primary site and you need your DR site to be active, you need to perform few changes in your environment to make DR site as active. Like DNS changes, HLB changes etc. Please check tool, i gave in my earlier post.

Apart from above, i highly advise you to hire Messaging Architect, who can help you in design HA solution for you. Or you can also take Microsoft PFE help.