SFTP, rsync all work, to some degree NFS also is an option.
However that's just the technology. You need to build a solution around it, which monitors load and deploys the code as needed and scales down again and eventually in PHP you'd also expect that PHP Session management is integrated ... all doable and people did. The selling point of lambda is "it works" and "not your concern" (with the corresponding downsides)
However that's just the technology. You need to build a solution around it, which monitors load and deploys the code as needed and scales down again and eventually in PHP you'd also expect that PHP Session management is integrated ... all doable and people did. The selling point of lambda is "it works" and "not your concern" (with the corresponding downsides)