In a scenario with two M Series routers in different data centers, very large portions of the configuration on the routers must be identical (for example, the entire configuration at the [edit services] hierarchy level).
To ensure that updates to certain portions of the configuration on one router are mirrored on the other, use the share-data.slax script in Junoscriptorium:
http://junoscriptorium.googlecode.com/svn/trunk/library/juniper/op/network/share-data/share-data.xml