Russia has a few military friends in its Collective Security Treaty Organisation (CSTO: members listed below). Iran has "observer" status in the organization.
The following excerpts are from the
CIA World Factbook
Russia
Religions:
Russian Orthodox 15-20%, Muslim 10-15%, other Christian 2% (2006 est.)
note: estimates are of practicing worshipers; Russia has large populations of non-practicing believers and non-believers, a legacy of over seven decades of Soviet rule
Kazakhstan
Religions:
Muslim 47%, Russian Orthodox 44%, Protestant 2%, other 7%
Kyrgyzstan
Religions:
Muslim 75%, Russian Orthodox 20%, other 5%
Tajikistan
Religions:
Sunni Muslim 85%, Shia Muslim 5%, other 10% (2003 est.)
Uzbekistan
Religions:
Muslim 88% (mostly Sunnis), Eastern Orthodox 9%, other 3%
Belarus
Background:
Government restrictions on freedom of speech and the press, peaceful assembly, and religion remain in place.
Religions:
Eastern Orthodox 80%, other (including Roman Catholic, Protestant, Jewish, and Muslim) 20% (1997 est.)
Armenia
Religions:
Armenian Apostolic 94.7%, other Christian 4%, Yezidi (monotheist with elements of nature worship) 1.3%