As you know, Israel periodically strikes on Syrian territory. These shocks are mainly applied for military purposes. The last such strike took place on Friday the 13th. (13 January 2017). This time, the aim of the Israeli strike was Mezzeh military airport near Damascus (5 km from the palace of Bashar al-Assad). It is reported that this airfield is used by the elite Guard forces of Assad.
Representatives of the Syrian regime naturally criticized Israel, but no actions were made as a response, they restricted themselves by a warning. The Syrians can be understood, in principle, considering the impotence of the Syrian Air Force and Air Defense, and the inability or unwillingness of the allies (Iran and Russia) to protect them, all they can do is nothing but “another warning”.
Though there has been a Russian complex S-400 “Triumph” in Syria since 2015, (which has no analogues in the world according to the assertions of the Russian side), to protect the “friend Assad” with its help the Russian side does not hurry.
I do not rule out that the aim of the Israeli attacks is the destruction of advanced weapons, transported to the Assad regime by allies, some of which are or may be forwarded to the Lebanese Shiite movement Hezbollah (we can’t exclude the desire of Israel to destroy as many high-ranking Iranian officers from elite units as possible).
As for the weapons, most likely, among the weapons which are destroyed by the Israelis, there are Russian arms transferred to Assad. But the Russian side is silent on this subject.
Although in 2013, Russian Foreign Minister Sergei Lavrov, commenting on the target of the Israeli attacks, said that: “According to our estimates, these goals, after all, are related to the operation of military defense system of the Syrian state.” 2017 is on the way, Israel is continuing strikes on the territory of Syria, including military installations. And when you consider that the “military-defense system of the Syrian state” is equipped with Russian weapons, it can be concluded that this weapon is ineffective against Israel, and suitable only for protection against much technologically backward opponents.
Hence, we can draw several conclusions;

1. Either Israel coordinates its activities with the Russian side (obviously there is some kind of tacit agreement between the two countries). Therefore, the Russian side indulges Israel, and is not eager to defend the military infrastructure of its ally Assad. In this case, Russian propaganda thesis becomes highly disputable that “Putin never gives up on his allies.” Because the situation seems to be twofold.

2. Or Russia, understanding the technical and tactical superiority of Israel, does not want to risk further the reputation of their weapons, and make enemies in the face of Israel entering into open conflict with this country.

3. Since Israel is mainly aiming at weakening Hezbollah and Iran, perhaps it is profitable for Moscow to squeeze out or at least not allow Iran to grow in the region by the hands of Israel.

Obviously someone else can put forward other versions, it is quite normal. On the other hand, it can be assumed that all three elements are present in this matter, and this assumption can also be considered.