There is no native clustering of Composer. The closest thing would be to deploy Cloud Pod Architecture (CPA).
Administering Cloud Pod Architecture in Horizon 7
With CPA you would need two or more pods each consisting of the following. You then configure a pool to span two pods, if one is down users will connect to the other.
- vCenter
- ESXi hosts
- Connection Servers
- UAG/Security Servers
- Composer