nss-mymachines, libnss_mymachines.so.2 - Hostname resolution for local container instances
nss-mymachines is a plug-in module for the GNU Name Service Switch (NSS) functionality of the GNU C Library (glibc), providing hostname resolution for the names of containers running locally that are registered with systemd-machined.service(8). The container names are resolved to the IP addresses of the specific container, ordered by their scope. This functionality only applies to containers using network namespacing (see the description of --private-network in systemd-nspawn(1)). Note that the name that is resolved is the one registered with systemd-machined, which may be different than the hostname configured inside of the container.
Note that this NSS module only makes available names of the containers running immediately below the current system context. It does not provide host name resolution for containers running side-by-side with the invoking system context, or containers further up or down the container hierarchy. Or in other words, on the host system it provides host name resolution for the containers running immediately below the host environment. When used inside a container environment however, it will not be able to provide name resolution for containers running on the host (as those are siblings and not children of the current container environment), but instead only for nested containers running immediately below its own container environment.
To activate the NSS module, add "mymachines" to the line starting with "hosts:" in /etc/nsswitch.conf.
It is recommended to place "mymachines" before the "resolve" or "dns" entry of the "hosts:" line of /etc/nsswitch.conf in order to make sure that its mappings are preferred over other resolvers such as DNS.
CONFIGURATION IN /ETC/NSSWITCH.CONF
Here is an example /etc/nsswitch.conf file that enables nss-mymachines correctly:
passwd: compat systemd group: compat [SUCCESS=merge] systemd shadow: compat systemd gshadow: files systemd hosts: mymachines resolve [!UNAVAIL=return] files myhostname dns networks: files protocols: db files services: db files ethers: db files rpc: db files netgroup: nis
EXAMPLE: MAPPINGS PROVIDED BY NSS-MYMACHINES
The container "rawhide" is spawned using systemd-nspawn(1):
# systemd-nspawn -M rawhide --boot --network-veth --private-users=pick Spawning container rawhide on /var/lib/machines/rawhide. Selected user namespace base 20119552 and range 65536. ... $ machinectl --max-addresses=3 MACHINE CLASS SERVICE OS VERSION ADDRESSES rawhide container systemd-nspawn fedora 30 169.254.40.164 fe80::94aa:3aff:fe7b:d4b9 $ ping -c1 rawhide PING rawhide(fe80::94aa:3aff:fe7b:d4b9%ve-rawhide (fe80::94aa:3aff:fe7b:d4b9%ve-rawhide)) 56 data bytes 64 bytes from fe80::94aa:3aff:fe7b:d4b9%ve-rawhide (fe80::94aa:3aff:fe7b:d4b9%ve-rawhide): icmp_seq=1 ttl=64 time=0.045 ms ... $ ping -c1 -4 rawhide PING rawhide (169.254.40.164) 56(84) bytes of data. 64 bytes from 169.254.40.164 (169.254.40.164): icmp_seq=1 ttl=64 time=0.064 ms ... # machinectl shell rawhide /sbin/ip a Connected to machine rawhide. Press ^] three times within 1s to exit session. 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
... 2: host0@if21: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
link/ether 96:aa:3a:7b:d4:b9 brd ff:ff:ff:ff:ff:ff link-netnsid 0
inet 169.254.40.164/16 brd 169.254.255.255 scope link host0
valid_lft forever preferred_lft forever
inet6 fe80::94aa:3aff:fe7b:d4b9/64 scope link
valid_lft forever preferred_lft forever Connection to machine rawhide terminated.
systemd(1), systemd-machined.service(8), machinectl(1), nss-systemd(8), nss-resolve(8), nss-myhostname(8), nsswitch.conf(5), getent(1)