Alastair, who turned pro with Edinburgh from Stirling County and Allan Glens, explained that the decision to make the move came down to a combination of rugby and personal issues.
"It was offered to me a while back and I thought long and hard about it," explained Alastair in the Daily Mail.
"I first spoke to Frank Hadden and Todd Blackadder about it a good few weeks ago now. I've had time to weigh up my options and I know it's the right move for me.
"It wasn't a case of getting more game time. Every single Edinburgh game I have been fit for this season, I've played in.
"If anything, it was because I could play loosehead lock, jump at No4 in the lineout and take charge of the lineout - I think I'm a better player in that position.
"There's also a number of factors outside rugby which make it beneficial for me to relocate. I stay in Livingston, my girlfriend Ashley works in Glasgow, so we'll be moving back to the city, while my family are in Bishopbriggs.
"Don't get me wrong. I've really enjoyed my time at Edinburgh. But this gives me an opportunity to have more leadership and to play in my preferred position.
"At Edinburgh, Scott Murray is in charge of the lineout and he's very good at it. But, as I said, I am looking for greater responsibility on the pitch and Sean Lineen has promised me I'll get that at Glasgow.
Alastair is in the Scotland squad to tour South Africa and he doesn't believe his international prosects will be dimmed by leaving Edinburgh for Glasgow.
"I won't know where I am until Frank makes it clear in his plans. I finished the Six Nations on the bench, but I have ambitions to become an established member of the Scotland team.
"If I thought that moving to Glasgow would harm my international chances, I would not have done so. Ultimately my goal is to play for Scotland and I see this as a chance to add to my experience.
"I will have Scott Lawson throwing to me at club level next season and that's another important aspect, as he is the incumbant Test hooker and we have made a good combination already.
"I am also used to working with Shade Munro (Glasgow and Scotland forwards coach) so it should be a relatively seamless transition.
With the current upheaval in Scottish rugby it could be said that Alastair, and Gunners teammate Francisco Lleonelli, are taking a risk in moving to Glasgow. With a Scottish pro team facing closure if a buyer can't be found careers appear more secure at SRU favourites, Edinburgh.
"I try not to worry about that," Alastair told the Daily Mail. "My focus is very much on the rugby and I hope thet the recruitment of myself and Francisco will demonstrate that Glasgow mean business next season.
"I spoke to Sean on a few occasions while I was making up my mind.
"Basically, Glasgow are a good team. They showed what they are capable of by putting 46 points on us at Firhill in the league. They've got outstanding young prospects in John Beattie and John Barclay and I am looking forward to playing alongside them."