  We present a long-term optical spectroscopic study of the post-AGB binary
system 89 Herculis, with the aim to characterize the relationship between
photospheric instabilities and dynamics in the close circumstellar environment
of the system. This study is based on spectra acquired with the high-resolution
Catania Astrophysical Observatory Spectropolarimeter and archive data, covering
a time interval between 1978 and 2018. We find long-term changes in the radial
velocity curve of the system, occurring mostly in amplitude, which correlate
with the variability observed in the blue-shifted absorption component of the P
Cygni like H$\alpha$ profile. Two possible scenarios are discussed. We also
find strong splitting in the s-process elements of \ion{Ba}{ii} $6141.713$ \AA\
and $6496.898$ \AA\,lines, with short-term morphological variations. A Gaussian
decomposition of such profiles allows us to distinguish four shell components,
two expanding and two in-falling toward the central star, which are subject to
the orbital motion of the system and are not affected by the long-term
instabilities. Finally, we find that the numerous metal lines in emission could
originate in regions of a structured circumbinary disk that have sizes
proportional to the energy of the corresponding upper level transition $\rm
E_{up}$. This study demonstrates the potential of long-term high-resolution
spectroscopy in linking together the instability processes occurring during the
late evolutionary stages of post-AGBs and the subsequent phase of PNe.
