  Gravastars have been considered as a feasible alternative to black holes in
the past couple of decades. Stable models of gravastar have been studied in
many of the alternative gravity theories besides standard General Relativity
(GR). The Rastall theory of gravity is a popular alternative to GR, specially
in the cosmological and astrophysical context. Here, we propose a stellar model
under the Rastall gravity following Mazur-Mottola's \cite{Mazur2001,Mazur2004}
conjecture. The gravastar consists of three regions, viz., ($I$) Interior
region, ($II$) Intermediate shell region, and ($III$) Exterior region. The
pressure within the interior core region is assumed with a constant negative
matter-energy density which provides a repulsive force over the entire thin
shell region. The shell is assumed to be made up of fluid of ultrarelativistic
plasma which follows the Zel'dovich's conjecture of stiff fluid
\cite{Zeldo1962,Zel'dovich1972}. It is also assumed that the pressure is
proportional to the matter-energy density according to Zel'dovich's conjecture,
which cancel the repulsive force exerted by the interior region. The exterior
region is completely vacuum which is described by the Schwarzschild-de Sitter
solution. Under all these specifications we obtain a set of exact and
singularity-free solutions of the gravastar model presenting several physically
valid features within the framework of Rastall gravity. The physical properties
of the shell region namely, the energy density, proper length, total energy and
entropy are explored. The stability of the gravastar model is investigated
using the surface redshift against the shell thickness and maximizing the
entropy of the shell within the framework of Rastall gravity.
