Joining a PC to the Synology domain is the same procedure as a Windows domain - and it fails for the same number-one reason: DNS. Get the order right and every PC joins first try.
Once the Synology domain exists, each Windows PC joins it with a short routine. The routine itself is five minutes; the failures people hit are almost never the routine - they are the preparation steps skipped before it. This page gives the order that works: DNS, clock, join, restart, verify.
The PC finds the domain controller by asking DNS for the domain name. If the PC's DNS server is the router's public forwarding address or 8.8.8.8, that question never reaches the NAS and the join dies with an Active Directory domain controller could not be contacted. Set the PC's DNS server to the NAS's static IP - ideally permanently, by configuring the router's DHCP to hand out the NAS as DNS. Prove it before continuing: nslookup office.local (your domain name) must return the NAS's address.
Kerberos, the login protocol, rejects authentication when the PC and the controller disagree about the time by more than a few minutes. A PC with a dead CMOS battery or a manually wrong clock will fail logins mysteriously after joining. Set the PC to automatic time, let it sync, then proceed.
sysdm.cpl, open the Computer Name tab and click Change.office.local), and click OK.At the login screen choose Other user and sign in with a domain account. Three checks confirm a healthy join: whoami shows DOMAIN\username; echo %USERDOMAIN% shows your domain, not the PC's own name; and Group Policy reaches the PC - run gpupdate /force and it should complete without a domain error. The computer account now also exists in Directory Server on the NAS, where you can see and manage it.
Controller could not be contacted: DNS, almost every time - repeat step 1 and the nslookup proof; also confirm the PC and NAS are on the same LAN with no guest-Wi-Fi isolation between them. Credentials rejected: you used a normal user or the local NAS admin - the join needs the domain administrator account. Network path not found: the PC resolved something wrong - check for an old hosts-file entry or a second DNS address overruling the NAS. Fix the layer the message names, then retry - do not reinstall anything.
The video joins machines to the live Synology domain - watch the sequence once and the steps above will feel familiar.
Watch Full VideoNo. Domain joining is a Pro-and-above Windows feature, exactly as with a Windows Server domain. Home edition PCs can still use NAS file shares with a domain account, but they cannot be domain members or receive Group Policy.
In nearly every case the PC is not using the Synology NAS as its DNS server. Set DNS to the NAS's static IP, confirm with nslookup that the domain name resolves to the NAS, and the join will normally succeed immediately.
For a small office, yes - it is a five-minute desk visit per PC, and it is also your moment to verify DNS and time settings on that machine. There is no supported bulk-join magic for a domain this size; the visit is the quality control.