Approximating Flexible Graph Connectivity via Räcke Tree based Rounding

Flexible graph connectivity is a new network design model introduced by Adjiashvili. It has seen several recent algorithmic advances. Despite these, the approximability even in the setting of a single-pair $(s,t)$ is poorly understood. In our recent work, we raised the question of whether there is poly-logarithmic approximation for the survivable network design version (Flex-SNDP) when the connectivity requirements are fixed constants. In this paper, we adapt a powerful framework for survivable network design recently developed by Chen, Laekhanukit, Liao, and Zhang to give an affirmative answer to the question. The framework of is based on Räcke trees and group Steiner tree rounding. The algorithm and analysis also establishes an upper bound on the integrality gap of an LP relaxation for Flex-SNDP.