This achievement can be confusing, so I thought i'd explain how I got it Solo Heroic.
First off this achievement is on Episode 5, Chapter 1 "Spartan Millar" and it must be done on Heroic or Legendary
You're allowed to die as many times as you want, even though the achievement description says "survive"
You're also allowed to lose 1 of the generators you defend, But not both!
Now first things first, clear out all the enemies until you have to activate 2 buttons on the ground, as soon as you activate these 2 buttons you are going to have to defend those points from taking damage. After you activate the first button a couple of crawlers will spawn, kill them before activating the second button, then activate the second button.
Now the defend section goes by Time NOT waves of enemies killed. The defend section goes for about 5 minutes and you will hear dialogue ever couple of minutes to know your progressing.
What I find easiest, is to kill all the enemies in the first wave but 2! Keep 2 enemies alive and distract them as best as you can for 5 mins, keeping 2 enemies alive stops the next wave from spawning. I recommend you keep 2 knights alive but crawlers work too. To distract the knights, try shooting near them or there head (Not to much that you kill them, just enough to get there attention) if one of them starts punching your generator, try push against him to get him off and shooting at him a little. I find I always lose 1 generator but never both using this strategy and i die every 10 seconds or so, everytime you die just sprint back and try get there attention again.
Now after you successful defend your new objective will be to press a 3rd button DO NOT PRESS THIS BUTTON until you've popped the achievement, you have too clear out all the enemies then go down to where you were defending the generators and another wave will spawn and another and another... I was killing wave after wave downstairs for about 20-30mins, it honestly seems endless but isn't, after you kill the last wave your achievement should pop before pressing the 3rd button.
I hope this helps out some people, of course this can be done co-op too and is probably easier :)