I have two asa 5540 and two internet lines from two different providers. I wanna create two contextes on the ASA's and assign a vpn server (site to site) on each context for each provider. My question is do i have to enable stateful failover to use active/active with the contexts or lan failover is enough?
VPN is not supported in multi-context mode unless you are talking about permitting IPSEC traffic through the contexts.
enable stateful failover if you do not want any interruptions during a failover event (as connection state information gets replicated to the standby firewall ) otherwise lan failover will suffice to replicate the configuration changes.