Whats this ROFL? SL helped Pakistan in 1971 war against India and allowed PAF to refuel its planes in Colombo. What was the result? India-Vietnam defence cooperation is more lethal than China-Sri Lanka ties. I know how jittery you would be feeling inside while reading this.
Sri Lanka is an independent nation. They can do what they please and you will NOT get anyone's support if you try to push your neighbors around. The world has been fooled for decades, but they are paying more attention to India's behavior nowadays.
Indo-Vietnam partnership could be destroyed by China in the blink of an eye, even if you were given a decade to catch up and coordinate.