8266:

[[http://pubsubclient.knolleary.net/|Arduino IDE client for MQTT on 8266]]

  * [[http://pubsubclient.knolleary.net/api.html#publish2|API docs]]

Mosquitto:

[[http://spin.atomicobject.com/2014/03/19/mqtt-protocol-ethernet/|getting started tutorial]]
[[http://nthn.me/posts/2012/mqtt.html|another getting started tutorial]]
[[http://mosquitto.org/documentation/|documentation]]
[[http://test.mosquitto.org/|mosquitto test server]]
mosquitto has a limit of the number of open connections as defined by ulimit -n. It defaults to 1024 but can be increased e.g. sudo ulimit -n 2048
  * make the limit setting permanent by editing /etc/security/limits.conf as explained [[https://singztechmusings.wordpress.com/2011/07/11/ulimit-how-to-permanently-set-kernel-limits-in-linux/|here]]
  * also change /etc/sysctl.conf with open file settings

explore limits as in [[https://lists.launchpad.net/mosquitto-users/msg00163.html|this thread]]\\

mosquitto client:


example pub call: mosquitto_pub -h filimin.no-ip.info -p 8883 -d -t hello/world -m "Hello World" --insecure --cafile /tmp/ca.crt -I ESP8266
  * -d enable debug messages
  * --insecure accept the certificate even if it doesn't match the host name
  * --cafile this must match the cafile on the server...and you can't do an SSL-encrypted call from the client apparently without this file.
  * -I ID prefix for client name

[[http://www.steves-internet-guide.com/mqtt-clean-sessions-example/|cleansession and the retain flag]]
  * //conclusion: it appears clean session only has meaning with QoS > 0//

erase all retained messages: mosquitto_sub -i <client_id> -p <port> -h <host> --retained-only -t "#" -v | while read line; do let "x=x+1"; echo $x; mosquitto_pub -i <client_id> -p <port> -h <host> -t "${line% *}" -r -n; done'
\\

===== HA Proxy: =====

==== Configuring for high # of connections (tested on 16.04) ====

edit ''/etc/sysctl.conf'' and add the following lines (increase open file limit and decrease memory use of TCP buffers:
<code>
fs.file-max = 10000000
fs.nr_open = 10000000
net.ipv4.tcp_mem = 786432 1697152 1945728
net.ipv4.tcp_rmem = 4096 4096 16777216
net.ipv4.tcp_wmem = 4096 4096 16777216
net.ipv4.ip_local_port_range = 15000 65535
</code>

edit /etc/security/limits.conf:
<code>
* soft nofile 10000000
* hard nofile 10000000
root soft nofile 10000000
root hard nofile 10000000
</code>

add to ''/etc/haproxy/haproxy.conf:'' in ''defaults:''
<code>
maxconn 2000000
timeout connect 3000000 # necessary?
timeout client 66000000 # necessary?
timeout server 66000000 # necessary?
</code> 

check:
<code>
pidof haproxy
cat /proc/630/limits | grep 'open files'
</code>

[[https://ma.ttias.be/linux-increase-ip_local_port_range-tcp-port-range/|increase ip_local_port_range]]

=== References ===

  * [[http://rexpie.github.io/2015/08/26/loadbalancing-with-haproxy.html|Load balancing with HA proxy]]
  * [[https://www.linangran.com/?p=547|Configuring HA proxy for 300k connections]]
  * [[https://serverfault.com/questions/669596/configure-haproxy-on-linux-to-accept-10k-simultaneous-connections|important tip I needed for getting beyond 2048 connections]]



[[https://github.com/lelylan/lelylan|Lelylan]] is an IoT framwork to making clustering etc. easier

  * [[https://github.com/lelylan/haproxy-mqtt/blob/master/haproxy.cfg|stuff about Lelylan with HAProxy]]

[[https://github.com/mqtt/mqtt.github.io/wiki/Server%20support|chart comparing MQTT brokers]]


[[https://serversforhackers.com/load-balancing-with-haproxy|complete article showing clustering with Mosca, HA Proxy and friends]]