Vishap doesn't have an aggro table, so there's no "tanking the boss". The boss follows a set pattern path.

The tanks are there to pick up adds which can be slowed and mowed down by the two (usually dps or a dps & a healer) on the cannons, plus the dps on the boss. Typically tanks will gather adds and gather them near the front of Vishap

At least one of the healers has to heal the group, depending on gear, you can get by with having one of the healers do the healing.

The two on the cannons will also need to use the snares on Vishap so that whomever is in charge of using the dragon killer can use it on the massive dragon (the first dragon killer has no snares).

There are a couple of adds that also do not have aggro tables (you'll recognize them as the giant turtles & the dragons that look like the last boss of Stone Vigil). These two adds use the same mechanics as their counterparts that you encountered as bosses in Stone Vigil (Hard). The cannoneers use the Spindly Fingers ability to stun the turtles from using their raid-wide AOE.

When Vishap is in range of the snares, the snares need to be used (ideally this should be up to those on the cannons). Once Vishap is in range and snared, the dragon killer is used. By the time you get to the 3rd (and last) snare, a DPS should use LB3.

Naturally, adjust your strategy based upon the make-up and capabilities of the raid.