Sri Lanka's main airport (Bandaranaike International) is going to be closed during the day until April 6th (starting this Friday, January 6th). It will only operate from 16.30 to 8.30.
This has to be done (the runway is 20 years old) but it means that you'll need to arrive 4-5 hours early for any flight, which sucks.
One plus is that the Airport published a quite detailed explanation, which also shares what an average day is like. On a usual day (when the airport is open) it handles 170 flights and 25,000 passengers. For a sense of scale, that's 1/10th the amount of daily traffic that the busiest airport in the world does. The Atlanta Airport handles nearly 275,000 people every day.
Basically, after 20 years of use, it's due for a makeover. There are already 'alligator' cracks appearing which could be a huge problem.
The authorities considered and rejected the following options as well:
Therefore, they decided to close the airport for this period.
For now, check in like it's the war days, arrive 4-5 hours early. Note that for SriLankan flights you must arrive at least 90 minutes before or they won't check you in at all. A lot of flights are canceled or shifted to other times (you can see the list for SriLankan here) and it will basically be uncomfortable for a while.