Not only Debian, but some other distro don’t install ifconfig by default in a minimal setup, including CentOS 7. It is still available in the net-tools package for CentOS 7 as part of the base repository, and I believe Debain should have it too, just not sure whether they use the same package name.
Newer distros moved to iproute package. The new ip command from this package now does ifconfig/route and many other tasks. To get IP address, just use ip addr (multiline output) or ip -o addr (single line output for each interface).