On a flat surface the ledger board is much simplier to attach, flash, and caulk than on a log curved surface.
So, I have not done this before, but I am visualizing the situation and goin from there. Others will jump in and add to it.
The important part is a good secure fasten to the most convex part of the log and to do what ever you can to flash and caulk and tar paper the best you can to retard rot and other stuff.
So, I would: fasten some heavy building paper to the log area that the ledge will be fixed to. Over that, I might install some 8 inch roll flashing over the paper and tack some roofing nails to hold in place. Then get some 3 1/2 inch galv or zinc coated lag screws with washers. Temp fasten the ledger to the log with drywall screws only to hold it to the wall as you drill pilot holes into the 2x10 and then into the log also. Go a size down from the actual lag. You do not want to split the log, the ledger will not anyway.
Drill these holes every 24 inches down the ledger.. Remove the temp screws and thread the lags with the washers into each hole so that about 1/2 inch protrudes so you can find the corresponding log hole.
Now run up the lags to secure the ledger into a tight fit, but before your all the way up, install some metal roof edging over the top of the ledger board, this will assist in channeling the water off the ledger and onto the ground.
When the ledger is sucked up, take that roll flashing that is sticking up over the top of the ledger on the log wall and with roofing nails tack this every 6 inches all the way down the log, before doing this fill the area behind the top of the flashing with butyl rubber caulk. Nail it up and it will seal.
your log should be protected.
Now use those handy hangers, metal and install them all along the ledger for the joists to sit into. Use the appropriate fasteners for these hangers.