  I discuss the thermodynamics-based derivation of the formula for the
entanglement entropy of a system of gluons. The derivation is based on an
approach where saturation and the Unruh effect were used to obtain and discuss
the entropy of gluons. The formula agrees, in the high-energy limit, up to a
numerical factor, with more recent results, where arguments based on the
density matrix and bipartition of the proton were used to obtain the formula. I
also discuss the relation of entropy as obtained in BFKL in DLL approximation
and with the application of the BK equation.
