IPC Connection

Connect client libraries to NSO with IPC.

Client libraries connect to NSO for inter-process communication (IPC) using Unix domain sockets (Local IPC) or TCP. By default, NSO uses Local IPC over a Unix domain socket at the path /tmp/nso/nso-ipc, controlled by the /ncs-config/ncs-local-ipc/path element in ncs.conf. If you change the socket path, you can tell clients to use the new path through the NCS_IPC_PATH environment variable. Clients must also have filesystem permission to access the IPC socket path, or they will not be able to communicate with the NSO daemon process. Local IPC requires clients to run on the same host as NSO; for clients running on a remote host, use TCP IPC instead.

Alternatively, NSO can be configured to use TCP sockets for IPC by setting /ncs-config/ncs-local-ipc/enabled to false and configuring the address and port through the /ncs-config/ncs-ipc-address/ip (default value 127.0.0.1) and /ncs-config/ncs-ipc-address/port elements in ncs.conf. If you change these values, you will likely need to configure the clients accordingly. Note that these values have security implications; see Security Issues. In particular, changing the address away from 127.0.0.1 may allow unauthenticated remote connections.

Many of the clients read the environment variable NCS_IPC_PATH to determine the Local IPC socket path, or NCS_IPC_ADDR and NCS_IPC_PORT for TCP IPC, but others might need source code changes. When both NCS_IPC_PATH and NCS_IPC_PORT are set, NCS_IPC_PATH takes precedence and TCP is not used. This is a list of clients that communicate with NSO and what needs to be done when the IPC configuration is changed.

Client	Changes required
Remote commands via the ncs command	Remote commands, such as ncs --reload, check the environment variables NCS_IPC_PATH and NCS_IPC_ADDR/NCS_IPC_PORT.
CLI tools	The Command Line Interface (CLI) client ncs_cli and similar commands, such as ncs_cmd and ncs_load, check the environment variables NCS_IPC_PATH and NCS_IPC_ADDR/NCS_IPC_PORT. Alternatively, many of them also support command-line options (e.g. -S for socket path).
CDB and MAAPI clients	The address or path supplied to Cdb.connect() and Maapi.connect() must be changed.
Data provider API clients	The address or path supplied to Dp constructor socket must be changed.
Notification API clients	The new address or path must be supplied to the socket for the Notif constructor.

To run more than one instance of NSO on the same host (which can be useful in development scenarios), each instance needs its own IPC socket. Set /ncs-config/ncs-local-ipc/path in ncs.conf to different values for each instance. If, instead, you are using TCP for IPC, set /ncs-config/ncs-ipc-address/port in ncs.conf to different values. In either case, you may also need to change the NETCONF and CLI over SSH ports under /ncs-config/netconf/transport and /ncs-config/cli/ssh by either disabling them or changing their values.

Restricting Access to the IPC Socket

By default, NSO uses Local IPC (Unix domain sockets) and relies on Unix filesystem permissions on the socket path to prevent unauthorized access. In case this is not sufficient, such as when using TCP IPC or untrusted users have shell access on the system where NSO runs, it is possible to further restrict the access to the IPC socket.

For Local IPC, you can leverage Unix filesystem permissions for the socket path to limit which OS users and groups can initiate connections to the socket. NSO may also perform additional authentication of the connecting users based on their UID; see Authenticating IPC Access.

For TCP sockets, you can enable an access check by setting the ncs.conf element /ncs-config/ncs-ipc-access-check/enabled to true, and specifying a filename for /ncs-config/ncs-ipc-access-check/filename. The file should contain a shared secret, i.e., a random (printable ASCII) character string. Clients connecting to the IPC socket will then be required to prove that they have knowledge of the secret through a challenge handshake before they are allowed access to the NSO functions provided via the IPC socket.

The access permissions on this file must be restricted via OS file permissions, such that it can only be read by the NSO daemon and client processes that are allowed to connect to the IPC socket. E.g. if both the daemon and the clients run as root, the file can be owned by root and have only "read by owner" permission (i.e. mode 0400). Another possibility is to have a group that only the daemon and the clients belong to, set the group ID of the file to that group, and have only "read by group" permission (i.e. mode 040).

To provide the secret to the client libraries and inform them that they need to use the access check handshake, you have to set the environment variable NCS_IPC_ACCESS_FILE to the full pathname of the file containing the secret. This is sufficient for all the clients mentioned above, i.e., there is no need to change the application code to support or enable this check.

The access check must be either enabled or disabled for both the daemon and the clients. E.g., if /ncs-config/ncs-ipc-access-check/enabled in ncs.conf is not set to true but clients are started with the environment variable NCS_IPC_ACCESS_FILE pointing to a file with a secret, the client connections will fail.