I know this is a tough one! I have worked as a nanny and as a day care worker in the past and now I am a mother. Each child handles separation differently, some children will cry for hours, others will be upset for only a few minutes, and some seem not to mind having mom or dad leave very much. I noticed in the daycare that, contrary to popular opinion, it did not seem to matter how often the children were in daycare (full time or part time care) or even how young they were when they started day care, (six weeks or six months or older) what really made the difference was their individual personality, and their developmental stage. All babies undergo separation anxiety (or a worsening of separation anxiety) at around 8 months old, but it can start sooner. Even babies who have happily gone to day care for months will suddenly cry more when mom or dad leaves them there.
At one year old, your baby is still in the difficult phase with separation. But the good news is that it will not last much longer! He can and will get better with separations! What you need more than anything is a good caregiver who will be understanding and kind to him, you do NOT want to leave him with someone who has little experience or 6 other babies to look after by herself. And personally, I do not agree with the "tough love" approach of ignoring a crying child and going about other tasks, that drove me crazy in the day care I worked in! I was known for holding the crying baby as much as humanly possible, sometimes I'd be in the rocking chair with two babies on my lap and a third one in front of me in a bouncy seat trying to rock and soothe all three at once! Being a nanny was much easier! If you can get a GOOD nanny and pay her well, that is the best child care option, but I understand if that is not possible, since I could not afford a nanny for myself these days!
Anyway, here is my routine for leaving a child, go into the day care room (or the playroom with the nanny) and play with your baby for a few minutes. Talk to the caregiver in a kind, happy voice so that your little one can see that you like and trust this person. If possible, get all three of you doing an activity together like playing with toy cars or building with blocks. Then say goodbye in a bright, happy voice, give hugs and kisses to your little one, and leave. Do not say goodbye and then stay for 10 more minutes, this will teach your son to cry hard to delay your leaving! But on the other end of the spectrum, do not just run him into the room and dash out as fast as you can either, he needs a couple of minutes of transition time. I thought it was great when parents could come for a visit during their lunch breaks, that way you can see how your son is doing and have some cuddle time, if he is still breastfeeding it is great to get an afternoon nursing session in. He will cry again when you leave, but I still think that it is worth it to have at least a little more mommy time. I also think it is a good idea, if possible, to take him to daycare for a couple of practice days before you start your job. Have him stay only for an hour or two without you to get used to the idea that you will leave him there, but you will come back again.
Best of luck!