PEN(1)PEN(1)NAMEpen - Load balancer for udp and tcp based protocols
SYNOPSISpen [-b sec] [-c N] [-e host:port] [-t sec] [-x N] [-j dir] [-u user]
[-F cfgfile] [-l logfile] [-p file ] [-w file] [-C
port|/path/to/socket] [-T sec] [-UHWXadfhrs] [-o option] [-E certfile]
[-K keyfile] [-G cacertfile] [-A cacertdir] [-Z] [-R] [-L protocol]
[host:]port|/path/to/socket h1[:p1[:maxc1[:hard1[:weight1[:prio1]]]]]
[h2[:p2[:maxc2[:hard2[:weight2[:prio2]]]]]] ...
Windows only:
pen-i service_name
pen-u service_name
EXAMPLEpen 80 www1:8000:10 www2:80:10 www3
Here three servers cooperate in a web server farm. Host www1 runs its
web server on port 8000 and accepts a maximum of 10 simultaneous con‐
nections. Host www2 runs on port 80 and accepts 10 connections.
Finally, www3 runs its web server on port 80 and allows an unlimited
number of simultaneous connections.
DESCRIPTION
Pen is a load balancer for tcp based protocols such as http or smtp. It
allows several servers to appear as one to the outside and automati‐
cally detects servers that are down and distributes clients among the
available servers. This gives high availability and scalable perfor‐
mance.
The load balancing algorithm keeps track of clients and will try to
send them back to the server they visited the last time. The client ta‐
ble has a number of slots (default 2048, settable through command-line
arguments). When the table is full, the least recently used one will be
thrown out to make room for the new one.
This is superior to a simple round-robin algorithm, which sends a
client that connects repeatedly to different servers. Doing so breaks
applications that maintain state between connections in the server,
including most modern web applications.
When pen detects that a server is unavailable, it scans for another
starting with the server after the most recently used one. That way we
get load balancing and "fair" failover for free.
Correctly configured, pen can ensure that a server farm is always
available, even when individual servers are brought down for mainte‐
nance or reconfiguration. The final single point of failure, pen
itself, can be eliminated by running pen on several servers, using vrrp
to decide which is active.
Sending pen a USR1 signal will make it print some useful statistics on
stderr, even if debugging is disabled. If pen is running in the back‐
ground (i.e. without the -f option), syslog is used rather than
stderr. If the -w option is used, the statistics is saved in HTML for‐
mat in the given file.
Sending pen a HUP signal will make it close and reopen the logfile, if
logging is enabled, and reload the configuration file.
Rotate the log like this (assuming pen.log is the name of the logfile):
mv pen.log pen.log.1 kill -HUP `cat <pidfile>`
where <pidfile> is the file containing pen's process id, as written by
the -p option.
Sending pen a TERM signal will make it exit cleanly, closing the log
file and all open sockets.
OPTIONS-C port|/path/to/socket
Specifies a control port where the load balancer listens for
commands. See penctl.1 for a list of the commands available. The
protocol is unauthenticated and the administrator is expected to
restrict access using an access control list (for connections
over a network) or Unix file permissions (for a Unix domain
socket). Pen will normally refuse to open the control port if
running as root; see -u option. If you still insist that you
want to run pen as root with a control port, use "-u root".
-F cfgfile
Names a configuration file with commands in penctl format (see
penctl.1). The file is read after processing all command line
arguments, and also after receiving a HUP signal.
-H Adds X-Forwarded-For header to http requests.
-U Use udp protocol support
-O command
Allows most penctl commands to be used on the Pen command line.
-P Use poll() for event notification.
-Q Use kqueue() for event notification (BSD).
-W Use weight for server selection.
-X Adds an exit command to the control interface.
-a Used in conjunction with -dd to get communication dumps in ascii
rather than hexadecimal format.
-b sec Servers that do not respond are blacklisted, i.e. excluded from
the server selection algorithm, for the specified number of sec‐
onds (default 30).
-T sec Clients are tracked for the specified number of seconds so they
can be sent to the same server as the last time (default 0 =
never expire clients).
-c N Max number of clients (default 2048).
-d Debugging (repeat -d for more). The output goes to stderr if we
are running in the foreground (see -f) and to syslog (facility
user, priority debug) otherwise.
-e host:port
host:port specifies the emergency server to contact if all regu‐
lar servers become unavailable.
-f Stay in foreground.
-h Use a hash on the client IP address for the initial server
selection. This makes it more predictable where clients will be
connected.
-i service_name
Windows only. Install pen as a service.
-j dir Run in a chroot environment.
-l file
Turn on logging.
-m multi_accept
Accept up to multi_accept incoming connections at a time.
-p file
Write the pid of the running daemon to file.
-q backlog
Allow the queue of pending incoming connections to grow up to a
maximum of backlog entries.
-r Go straight into round-robin server selection without looking up
which server a client used the last time.
-s Stubborn server selection: if the initial choice is unavailable,
the client connection is closed without trying another server.
-t sec Connect timeout in seconds (default 5).
-u user
Posix only. Run as a different user.
-u service_name
Windows only. Uninstall the service.
-x N Max number of simultaneous connections (default 500).
-w file
File for status reports in HTML format.
-o option
Use option in penctl format.
-E certfile
Use the given certificate in PEM format.
-K keyfile
Use the given key in PEM format (may be contained in cert).
-G cacertfile
File containing the CA's certificate.
-A cacertdir
Directory containing CA certificates in hashed format.
-Z Use SSL compatibility mode.
-R Require valid peer certificate.
-L protocol
ssl23 (default), ssl3 or tls1.
[host:]port OR /path/to/socket
The local address and port pen listens to. By default pen lis‐
tens to all local addresses. Pen can also use a Unix domain
socket as the local listening address.
h1:p1:soft:hard:weight:prio
The address, port and maximum number of simultaneous connections
for a remote server. By default, the port is the same as the
local port, and the soft limit on the number of connections is
unlimited. The hard limit is used for clients which have
accessed the server before. The weight and prio are used for
the weight- and priority-based server selection algorithms.
LIMITATIONS
Pen runs in a single process, and opens two sockets for each connec‐
tion. Depending on kernel configuration, pen can run out of file
descriptors.
SSL support is available if pen was built with the --with-ssl option.
GeoIP support is available if pen was built with the --with-geoip
option.
SEE ALSOpenctl(1), dwatch(1), mergelogs(1), webresolve(1)AUTHOR
Copyright (C) 2001-2015 Ulric Eriksson, <ulric@siag.nu>.
ACKNOWLEDGEMENTS
In part inspired by balance by Thomas Obermair.
LOCAL PEN(1)
