random effect in GLMM

I have an issue with GLMM and random factors. I have 3 experimental sites but with different number of experimental units within each site. One site has 3 replicates of the treatment, 1 has 2 and the last one just has 1. I would like to know if I can set the site and/or replicate nested within each site as random factors even with this unbalanced design? Thank you for your help!! best regards.