I wanted to share knowledge of tuning FreeBSD via sysctl.conf / loader.conf
/ KENCONF / etc. It was initially based on Igor Sysoev's (author of nginx)
presentation about FreeBSD tuning up to 100,000-200,000 active connections.
Newer versions of FreeBSD can handle much much more.
Tunings are for FreeBSD7 - FreeBSD-CURRENT. Since 7.2 amd64 some of them are
tuned well by default. Prior 7.0 some of them are boot only (set via
/boot/loader.conf) or do not exist at all.
sysctl.conf:
# No zero mapping feature
# May break wine
# (There are also reports about broken samba3)
#security.bsd.map_at_zero=0
# Servers with threading software apache2 / Pound may want to rise following sysctl
#kern.threads.max_threads_per_proc=4096
# Max backlog size
# Note Application can still limit it by passing second argument to listen(2) syscall
# Note: Listen queue be monitored via `netstat -Lan`
kern.ipc.somaxconn=4096
# Shared memory
# Note: Only FreeBSD 7.2+ can use shared memory > 2Gb
#kern.ipc.shmmax=2147483648
# Sockets
kern.ipc.maxsockets=204800
# Mbuf 2k clusters (on amd64 7.2+ 25600 is default)
# Note: defaults for other variables depend on this variable, for example `tcpreass`
# Note: FreeBSD-7 and older: For such high value vm.kmem_size must be increased to 3G
kern.ipc.nmbclusters=262144
# Jumbo pagesize(_SC_PAGESIZE)/9k/16k clusters
# Used as general packet storage for jumbo frames on some network cards
# Can be monitored via `netstat -m`
#kern.ipc.nmbjumbop=262144
#kern.ipc.nmbjumbo9=65536
#kern.ipc.nmbjumbo16=32768
# For lower latency you can decrease schedulers maximum time slice
# default: stathz/10 (~ 13)
kern.sched.slice=1
# Increase max command-line length showed in `ps` (e.g for Tomcat/Java)
# Default is PAGE_SIZE / 16 or 256 on x86
# This avoids commands to be presented as [executable] in `ps`
# For more info see: http://www.freebsd.org/cgi/query-pr.cgi?pr=120749
kern.ps_arg_cache_limit=4096
# Every socket is a file, so increase them
kern.maxfiles=204800
kern.maxfilesperproc=200000
kern.maxvnodes=200000
# On some systems HPET is almost 2 times faster than default ACPI-fast
# Useful on systems with lots of clock_gettime / gettimeofday calls
# See http://old.nabble.com/ACPI-fast-default-timecounter,-but-HPET-83--faster-td23248172.html
# After revision 222222 HPET became default: http://svnweb.freebsd.org/base?view=revision&revision=222222
#kern.timecounter.hardware=HPET
# Small receive space, only usable on http-server
# Note: fileservers should increase it to 65535 or even more
#net.inet.tcp.recvspace=8192
# This is useful on Fat-Long-Pipes
#kern.ipc.maxsockbuf=10485760
#net.inet.tcp.recvbuf_max=10485760
#net.inet.tcp.recvbuf_inc=65535
# Small send space is useful for http servers that serve small files
# Note: Autotuned since 7.x
#net.inet.tcp.sendspace=16384
# This is useful on Fat-Long-Pipes
#net.inet.tcp.sendbuf_max=10485760
#net.inet.tcp.sendbuf_inc=65535
# Turn off send/receive autotuning if think you know better.
#net.inet.tcp.recvbuf_auto=0
#net.inet.tcp.sendbuf_auto=0
# This should be enabled if you going to use big spaces (>64k)
# Also timestamp field is useful when using syncookies
net.inet.tcp.rfc1323=1
# Turn this off on high-speed, lossless connections (LAN 1Gbit+)
#net.inet.tcp.delayed_ack=0
# This feature is useful if you are serving data over modems, Gigabit Ethernet,
# or even high speed WAN links (or any other link with a high bandwidth delay product),
# especially if you are also using window scaling or have configured a large send window.
# Automatically disables on small RTT ( http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/netinet/tcp_subr.c?#rev1.237 )
# This sysctl was removed in 10-CURRENT:
# See: http://www.mail-archive.com/svn-src-head@freebsd.org/msg06178.html
#net.inet.tcp.inflight.enable=0
# TCP slowstart algorithm tunings
# Here we are assuming VERY uncongested network
# Note: Only takes effect if net.inet.tcp.rfc3390 is set to 0,
# otherwise formula taken from http://tools.ietf.org/html/rfc3390
#net.inet.tcp.slowstart_flightsize=10
#net.inet.tcp.local_slowstart_flightsize=100
# Disable randomizing of ports to avoid false RST
# Before use check SA here www.bsdcan.org/2006/papers/ImprovingTCPIP.pdf
# Note: Port randomization autodisables at high connection rates
#net.inet.ip.portrange.randomized=0
# Increase portrange
# For outgoing connections only. Good for seed-boxes and ftp servers.
net.inet.ip.portrange.first=1024
net.inet.ip.portrange.last=65535
# Dtops route cache degradation during a DDoS.
# http://www.freebsd.org/doc/en/books/handbook/securing-freebsd.html
#net.inet.ip.rtexpire=2
net.inet.ip.rtminexpire=2
net.inet.ip.rtmaxcache=1024
# Security
net.inet.ip.redirect=0
net.inet.ip.sourceroute=0
net.inet.ip.accept_sourceroute=0
net.inet.icmp.maskrepl=0
net.inet.icmp.log_redirect=0
net.inet.icmp.drop_redirect=1
net.inet.tcp.drop_synfin=1
#
# There is also good example of sysctl.conf with comments:
# http://www.thern.org/projects/sysctl.conf
#
# icmp may NOT rst, helpful for those pesky spoofed
# icmp/udp floods that end up taking up your outgoing
# bandwidth/ifqueue due to all that outgoing RST traffic.
#
#net.inet.tcp.icmp_may_rst=0
# Security
# Do not send responses on attempts to connect to the closed ports
#net.inet.udp.blackhole=1
#net.inet.tcp.blackhole=2
# IPv6 Security
# For more info see http://www.fosslc.org/drupal/content/security-implications-ipv6
# Disable Node info replies
# To see this vulnerability in action run `ping6 -a sglAac ::1` or `ping6 -w ::1` on unprotected node
net.inet6.icmp6.nodeinfo=0
# Turn on IPv6 privacy extensions
# For more info see proposal http://unix.derkeiler.com/Mailing-Lists/FreeBSD/net/2008-06/msg00103.html
net.inet6.ip6.use_tempaddr=1
net.inet6.ip6.prefer_tempaddr=1
# Disable ICMP redirect
net.inet6.icmp6.rediraccept=0
# Disable acceptation of RA and auto link-local generation if you don't use them
#net.inet6.ip6.accept_rtadv=0
#net.inet6.ip6.auto_linklocal=0
# Increases default TTL
# Default is 64
#net.inet.ip.ttl=128
# Lessen max segment life to conserve resources
# ACK waiting time in milliseconds
# (default: 30000. RFC from 1979 recommends 120000)
net.inet.tcp.msl=5000
# Max number of time-wait sockets
net.inet.tcp.maxtcptw=200000
# Don't use tw on local connections
# As of 15 Apr 2009. Igor Sysoev says that nolocaltimewait has some buggy implementaion.
# So disable it or now till get fixed
#net.inet.tcp.nolocaltimewait=1
# FIN_WAIT_2 state fast recycle
net.inet.tcp.fast_finwait2_recycle=1
# Time before tcp keepalive probe is sent
# default is 2 hours (7200000)
#net.inet.tcp.keepidle=60000
# Use HTCP congestion control (don't forget to load cc_htcp kernel module)
net.inet.tcp.cc.algorithm=htcp
# Should be increased until net.inet.ip.intr_queue_drops is zero
net.inet.ip.intr_queue_maxlen=4096
# Protocol decoding in interrupt thread.
# If you have NIC that automatically sets flow_id then it's better to not
# use direct_force, and use advantages of multithreaded netisr(9)
# If you have Yandex drives you better off with `net.isr.direct_force=1` and
# `net.inet.tcp.read_locking=0` otherwise you may run into some TCP related
# problems.
# Note: If you have old NIC that don't set flow_ids you may need to
# patch `ip_input` to manually set FLOW_ID via `nh_m2flow`.
#
# FreeBSD 8+
#net.isr.direct=1
#net.isr.direct_force=1
# In FreeBSD 9+ it was renamed to
#net.isr.dispatch=direct
# This is for routers only
#net.inet.ip.forwarding=1
#net.inet.ip.fastforwarding=1
# This speed ups dummynet when channel isn't saturated
net.inet.ip.dummynet.io_fast=1
# Increase dummynet(4) hash
#net.inet.ip.dummynet.hash_size=65535
#net.inet.ip.dummynet.max_chain_len=8
# Should be increased when you have A LOT of files on server
# (Increase until vfs.ufs.dirhash_mem becomes lower)
vfs.ufs.dirhash_maxmem=67108864
# Note from commit http://svn.freebsd.org/base/head@211031 :
# For systems with RAID volumes and/or virtualization environments, where
# read performance is very important, increasing this sysctl tunable to 32
# or even more will demonstratively yield additional performance benefits.
vfs.read_max=32
# Explicit Congestion Notification
# (See http://en.wikipedia.org/wiki/Explicit_Congestion_Notification)
net.inet.tcp.ecn.enable=1
# Flowtable - flow caching mechanism
# Useful for routers
#net.inet.flowtable.enable=1
#net.inet.flowtable.nmbflows=65535
# IPFW dynamic rules and timeouts tuning
# Increase dyn_buckets till net.inet.ip.fw.curr_dyn_buckets is lower
net.inet.ip.fw.dyn_buckets=65536
net.inet.ip.fw.dyn_max=65536
net.inet.ip.fw.dyn_ack_lifetime=120
net.inet.ip.fw.dyn_syn_lifetime=10
net.inet.ip.fw.dyn_fin_lifetime=2
net.inet.ip.fw.dyn_short_lifetime=10
# Make packets pass firewall only once when using dummynet
# i.e. packets going thru pipe are passing out from firewall with accept
#net.inet.ip.fw.one_pass=1
# shm_use_phys Wires all shared pages, making them unswappable
# Use this to lessen Virtual Memory Manager's work when using Shared Mem.
# Useful for databases
#kern.ipc.shm_use_phys=1
# ZFS
# Enable prefetch. Useful for sequential load type i.e fileserver.
# FreeBSD sets vfs.zfs.prefetch_disable to 1 on any i386 systems and
# on any amd64 systems with less than 4GB of available memory
# See: http://old.nabble.com/Samba-read-speed-performance-tuning-td27964534.html
#vfs.zfs.prefetch_disable=0
# On highload servers you may notice following message in dmesg:
# "Approaching the limit on PV entries, consider increasing either the
# vm.pmap.shpgperproc or the vm.pmap.pv_entry_max tunable"
vm.pmap.shpgperproc=2048
loader.conf:
# Accept filters for data, http and DNS requests
# Useful when your software creates process/thread on each request (i.e. apache)
# Note: DNS accf available on 8.0+
# Note: In case of badly written software this can increase performance,
# but I still would recommend against using accept filters in production because of
# their opacity - they really break abstractions. Also it's not trivial to debug/monitor
# their state.
#accf_data_load="YES"
#accf_http_load="YES"
#accf_dns_load="YES"
# Async IO system calls
aio_load="YES"
# Linux specific devices in /dev
# As for 8.1 it only /dev/full
#lindev_load="YES"
# Adds NCQ support in FreeBSD
# WARNING! all ad[0-9]+ devices will be renamed to ada[0-9]+
# 8.0+ only
#ahci_load="YES"
#siis_load="YES"
# FreeBSD 9+
# New Congestion Control for FreeBSD
cc_htcp_load="YES"
#cc_cubic_load="YES"
# Increase kernel memory size to 3G.
#
# Use ONLY if you have KVA_PAGES in kernel configuration, and you have more than 3G RAM
# Otherwise panic will happen on next reboot!
#
# It's required for high buffer sizes: kern.ipc.nmbjumbop, kern.ipc.nmbclusters, etc
# Useful on highload stateful firewalls, proxies or ZFS fileservers
# (FreeBSD 7.2+ amd64 users: Check that current value is lower!)
#vm.kmem_size="3G"
# If you have really busy forking webserver (i.e. apache13) you may run out of processes
#kern.maxproc=10000
# If your server has lots of swap (>4Gb) you should increase following value
# according to http://lists.freebsd.org/pipermail/freebsd-hackers/2009-October/029616.html
# Otherwise you'll be getting errors
# "kernel: swap zone exhausted, increase kern.maxswzone"
#kern.maxswzone="256M"
# Older versions of FreeBSD can't tune maxfiles on the fly
#kern.maxfiles="200000"
# Useful for databases
# Sets maximum data size to 1G
# (FreeBSD 7.2+ amd64 users: Check that current value is lower!)
#kern.maxdsiz="1G"
# Maximum buffer size(vfs.maxbufspace)
# You can check current one via vfs.bufspace
# Should be lowered/upped depending on server's load-type
# Usually decreased to preserve kmem
# (default is 10% of mem)
#kern.maxbcache="512M"
# Sendfile buffers
# Note: i386 only
#kern.ipc.nsfbufs=10240
# syncache tuning
net.inet.tcp.syncache.hashsize=32768
net.inet.tcp.syncache.bucketlimit=32
net.inet.tcp.syncache.cachelimit=1048576
# Send RST on listen queue overflow / memory shortage.
# Hosts behind Load-Balancer should set it to 1 to fail fast.
# Hosts facing clients should set it to 0 for client to retry connection.
#net.inet.tcp.syncache.rst_on_sock_fail=0
# Increased hostcache
# Later host cache can be viewed via net.inet.tcp.hostcache.list hidden sysctl
# Very useful for it's RTT RTTVAR
# Must be power of two
net.inet.tcp.hostcache.hashsize=65536
# hashsize * bucketlimit (which is 30 by default)
# It allocates 255Mb (1966080*136) of RAM
net.inet.tcp.hostcache.cachelimit=1966080
# TCP control-block Hash table tuning
# See: http://serverfault.com/questions/372512/why-change-net-inet-tcp-tcbhashsize-in-freebsd
net.inet.tcp.tcbhashsize=524288
# Disable ipfw deny all
# Should be uncommented when there is a chance that
# kernel and ipfw binary may be out-of sync on next reboot
#net.inet.ip.fw.default_to_accept=1
#
# SIFTR (Statistical Information For TCP Research) is a kernel module that
# logs a range of statistics on active TCP connections to a log file.
# See prerelease notes:
# http://groups.google.com/group/mailing.freebsd.current/browse_thread/thread/b4c18be6cdce76e4
# and man 4 sitfr
#siftr_load="YES"
# Enable superpages, for 7.2+ only
# See: http://lists.freebsd.org/pipermail/freebsd-hackers/2009-November/030094.html
vm.pmap.pg_ps_enabled=1
# Useful if you are using Intel-Gigabit NIC
#hw.em.rxd=4096
#hw.em.txd=4096
#hw.em.rx_process_limit=-1
# Also if you have A LOT interrupts on NIC - play with following parameters
# NOTE: You should set them for every NIC
#dev.em.0.rx_int_delay: 250
#dev.em.0.tx_int_delay: 250
#dev.em.0.rx_abs_int_delay: 250
#dev.em.0.tx_abs_int_delay: 250
# There is also multithreaded version of em/igb drivers that can be found here:
# http://people.yandex-team.ru/~wawa/
#
# for additional em monitoring and statistics use
# sysctl dev.em.0.stats=1 ; dmesg
# sysctl dev.em.0.debug=1 ; dmesg
# Also after r209242 (-CURRENT) there is a separate sysctl for each stat variable;
# Same tunings for igb
#hw.igb.rxd=4096
#hw.igb.txd=4096
#hw.igb.rx_process_limit=-1
# Some useful netisr tunables. See sysctl net.isr
#net.isr.maxthreads=4
#net.isr.defaultqlimit=10240
#net.isr.maxqlimit=10240
# Bind netisr threads to CPUs
#net.isr.bindthreads=1
#
# FreeBSD 9.x+
# Increase interface send queue length
# See commit message http://svn.freebsd.org/viewvc/base?view=revision&revision=207554
#net.link.ifqmaxlen=1024
# Nicer boot logo =)
loader_logo="beastie"
And finally here is KERNCONF:
# Just some of them, see also
# cat /sys/{i386,amd64,}/conf/NOTES
# This one useful only on i386
#options KVA_PAGES=512
# From UPDATING 20121223:
# After switching to Clang as the default compiler some users of ZFS
# on i386 systems started to experience stack overflow kernel panics.
# Please consider using 'options KSTACK_PAGES=4' in such configurations.
#options KSTACK_PAGES=4
# You can play with HZ in environments with high interrupt rate (default is 1000)
# 100 is for my notebook to prolong it's battery life
#options HZ=100
# Eliminate datacopy on socket read-write
# To take advantage with zero copy sockets you should have an MTU >= 4k
# This req. is only for receiving data.
# Read more in man zero_copy_sockets
# Also this epic thread on kernel trap:
# http://kerneltrap.org/node/6506
# In conclusion Linus says:
# "anybody that does it that way (FreeBSD) is totally incompetent"
#
# Also see /usr/src/UPDATING 20121023 for notes about
# SOCKET_SEND_COW and SOCKET_RECV_PFLIP
#options ZERO_COPY_SOCKETS
# Support TCP sign. Used for IPSec
options TCP_SIGNATURE
# There was stackoverflow found in KAME IPSec stack:
# See http://secunia.com/advisories/43995/
# For quick workaround you can use `ipfw add deny proto ipcomp`
options IPSEC
# This ones can be loaded as modules. They described in loader.conf section
#options ACCEPT_FILTER_DATA
#options ACCEPT_FILTER_HTTP
# Adding ipfw, also can be loaded as modules
options IPFIREWALL
# On 8.1+ you can disable verbose to see blocked packets on ipfw0 interface.
# Also there is no point in compiling verbose into the kernel, because
# now there is net.inet.ip.fw.verbose tunable.
#options IPFIREWALL_VERBOSE
#options IPFIREWALL_VERBOSE_LIMIT=10
# The IPFIREWALL_FORWARD kernel option has been removed. Its
# functionality now turned on by default.
#options IPFIREWALL_FORWARD
# Adding kernel NAT
options IPFIREWALL_NAT
options LIBALIAS
# Traffic shaping
options DUMMYNET
# Divert, i.e. for userspace NAT
options IPDIVERT
# This is for OpenBSD's pf firewall
device pf
device pflog
# pf's QoS - ALTQ
options ALTQ
options ALTQ_CBQ # Class Bases Queuing (CBQ)
options ALTQ_RED # Random Early Detection (RED)
options ALTQ_RIO # RED In/Out
options ALTQ_HFSC # Hierarchical Packet Scheduler (HFSC)
options ALTQ_PRIQ # Priority Queuing (PRIQ)
options ALTQ_NOPCC # Required for SMP build
# Pretty console
# Manual can be found here http://forums.freebsd.org/showthread.php?t=6134
#options VESA
#options SC_PIXEL_MODE
# Disable reboot on Ctrl Alt Del
#options SC_DISABLE_REBOOT
# Change normal|kernel messages color
options SC_NORM_ATTR=(FG_GREEN|BG_BLACK)
options SC_KERNEL_CONS_ATTR=(FG_YELLOW|BG_BLACK)
# More scroll space
options SC_HISTORY_SIZE=8192
# Adding hardware crypto device
device crypto
device cryptodev
# Useful network interfaces
device vlan
device tap #Virtual Ethernet driver
device gre #IP over IP tunneling
device if_bridge #Bridge interface
device pfsync #synchronization interface for PF
device carp #Common Address Redundancy Protocol
device enc #IPsec interface
device lagg #Link aggregation interface
device stf #IPv4-IPv6 port
# Also for my notebook, but may be used with Opteron
device amdtemp
# Same for Intel processors
device coretemp
# man 4 cpuctl
device cpuctl # CPU control pseudo-device
# Support for ECMP. More than one route for destination
# Works even with default route so one can use it as LB for two ISP
# For now code is unstable and panics (panic: rtfree 2) on route deletions.
#options RADIX_MPATH
# Multicast routing
#options MROUTING
#options PIM
# Debug & DTrace
options KDB # Kernel debugger related code
options KDB_TRACE # Print a stack trace for a panic
options KDTRACE_FRAME # amd64-only(?)
options KDTRACE_HOOKS # all architectures - enable general DTrace hooks
#options DDB
#options DDB_CTF # all architectures - kernel ELF linker loads CTF data
# Adaptive spining in lockmgr (8.x+)
# See http://www.mail-archive.com/svn-src-all@freebsd.org/msg10782.html
options ADAPTIVE_LOCKMGRS
# UTF-8 in console (8.x+)
#options TEKEN_UTF8
# FreeBSD 8.1+
# Deadlock resolver thread
# For additional information see http://www.mail-archive.com/svn-src-all@freebsd.org/msg18124.html
# (FYI: "resolution" is panic so use with caution)
#options DEADLKRES
# Increase maximum size of Raw I/O and sendfile(2) readahead
#options MAXPHYS=(1024*1024)
#options MAXBSIZE=(1024*1024)
# For scheduler debug enable following option.
# Debug will be available via `kern.sched.stats` sysctl
# For more information see http://svnweb.freebsd.org/base/head/sys/conf/NOTES?view=markup
#options SCHED_STATS
# A framework for very efficient packet I/O from userspace, capable of
# line rate at 10G (FreeBSD10+)
# See http://svnweb.freebsd.org/base?view=revision&revision=227614
#device netmap
If you are tuning network for maximum performance you may wish to play with
ifconfig options like:
# You can list all capabilities via `ifconfig -m`
ifconfig [-]rxcsum [-]txcsum [-]tso [-]lro mtu
In case you've enabled DDB in kernel config, you should edit your
/etc/ddb.conf and add something like this to enable automatic reboot (and
textdump as bonus):
script kdb.enter.panic=textdump set; capture on; show pcpu; bt; ps; alltrace; capture off; call doadump; reset
script kdb.enter.default=textdump set; capture on; bt; ps; capture off; call doadump; reset
And do not forget to add ddb_enable="YES" to /etc/rc.conf
Since FreeBSD 9 you can select to enable/disable flowcontrol on your NIC:
# See http://en.wikipedia.org/wiki/Ethernet_flow_control and
# http://www.mail-archive.com/svn-src-head@freebsd.org/msg07927.html for additional info
ifconfig bge0 media auto mediaopt flowcontrol
Most of FreeBSD's limits can be monitored by:
# vmstat -z
and
# limits
Variety of network counters can be monitored via
# netstat -s
In FreeBSD-8+ netstat's -Q option appeared, try following command to display
netisr stats
# netstat -Q
For solving non-trivial TCP problems one can use net.inet.tcp.log_debug, it
produces dmesg output similar to:
host kernel: TCP: [0.0.0.0]:0 to [1.1.1.1]:1; syncache_socket: Socket create failed due to limits or memory shortage
host kernel: TCP: [0.0.0.0]:0 to [1.1.1.1]:1 tcpflags 0x10<ACK>; tcp_input: Listen socket: Socket allocation failed due to limits or memory shortage, sending RST
NB!
Last but not the least: if you are into network tuning - it's good
practice to buy the best network card you can afford. I personally prefer
Intel's igb(4), list of models can be found in if_igb.c
PS. also see
# man 7 tuning
And FreeBSD Wiki on network performance tuning made by developers themselves.
PPS. Calomel.org - Open Source Research and Reference blog has nice write up about network performance and recent article about FreeBSD Tuning and Optimization.
Thanks
I wanted to thank FreeBSD community, especially author of nginx - Igor
Sysoev, nginx-ru@ and FreeBSD-performance@ mailing lists for providing useful
information about FreeBSD tuning. Yandex BSD lovers from noc@ and
search-admin@, especially melifaro@ and zont@.
Disclaimer
This is definitely not something that you should copy/paste into your production
configs! Some of provided "tunings" can be even harmful. Use provided data as
reference for further investigation or A/B testing. I say it again just to be
explicit: DO NOT BLINDLY APPLY "TUNINGS" YOU'VE FOUND ON INTERNET!.
Before applying any sysctl on production system you should investigate it's
impact (it's essential to look in kernel's source code) and measure it's
performance benefits(if any) in testing environment.
Use this post at your own risk.
FreeBSD WIP
* Whats cooking for FreeBSD 7?
* Whats cooking for FreeBSD 8?
* Whats cooking for FreeBSD 9?
* What's new for FreeBSD 10?
* What's new for FreeBSD 11?
Question to viewers
What tunings are you using on yours FreeBSD servers?
You can also post your /etc/sysctl.conf, /boot/loader.conf, kernel options,
etc with description of its' meaning (do not copy-paste from sysctl -d).
Don't forget to specify server type (frontend, backend, cache, db, storage,
gateway, etc)
Let's share experience!
