This post is describing how to setup a Mongo Db database in a clustering mode. I choose to deploy 3 replica set on 3 different bare metal server running centos 7 and to add 1 arbiter to reduce vote problem during a server crash or reboot.
You will find the different steps to make this configuration running, the way to secure it in a vlan and to activate the authentication.
I also added some elements on the way to backup it. Feel free to propose enhancement and links in the comments.
This is a recurrent operation I’m doing regularly these time : extending a Linux partition by adding new virtual disk I’ve attached to a growing VM. Nothing fantastic to expect in this post. Its purpose is to keep on my hand the solution I’ve used to stop searching google and getting a different one every time ;).
This tuto is applicable for centos 7. The content will be updated when I’ll have to perform different operations.
You may have read some of my post about RF433 and Raspberry PI. Basically with RPI 1, I was using wiringPi interrupt handler to manage the RF433 decoding. The problem is that with RPI2 and RPI B+ the delay to take an interrupt that was becomes unpredictable. And the timing constraints are not respected. As a consequence part of the messages are loss because for these delay.
One of the solution (the software one) is to be more efficient to proceed the interrupts and the way to do this is to compile a kernel driver for directly handling the interrupts. This is what this post is about. This comes to complete the RFRPI code and associated hardware. A complete source code and software for using it is on the rfrpi bitbucket repository.
Challenge of the coming days : write a kernel driver to manage interruption quicker on a raspberry pi 2. I’m happy to find a lot of example on Internet and in particular this one, that is really looking like what I’m trying to do. This post is describing all the step needed to do this.
The new version of kernel now activate the device-tree standard, it means that instead of having all module activated by default with some stopped by a blacklist system, now, all are disable and activated only when described in a device tree.
Device tree details the system architecture and dependencies following configuration files. The device tree can be owned by the shield itself in an attached eprom.
As a consequence, now, i2c / spi are not activated by default. So if you need to activate it on startup. For this, edit /boot/config.txt and add line at the end like :
dtparam=i2c_arm=on # for i2c 1 dtparam=i2c_vc=on # for i2c 0 dtparam=spi=on dtparam=i2s=on dtparam=i2c_arm=on,i2c_vc=on
Then reboot
CentOS 7 have selinux activated, so when you decide to change your default httpd directories you have to give the right selinux permission to these directories otherwize the https server will not be able to access the files.
CentOs 7 have a built-in configuration to close the inactive ssh session. In term of security it is a good thing but when killing a session after 1 minute of inactivity start to be a mess when you have multiple session opened in parallel.
This can be avoid on the client side by configuring a keep-alive period on the client side. To activate a such keepalive, you just have to connect with the following command line:
ssh -o ServerAliveInterval=5 login@server.com
This will configure client to send a NULL packet every 5 seconds to keep the session opened.
If you try to access a remote database with nginx or httpd server, you will have a connection problem with error code (13) even if mysql/mariadb client works well in command line. The reason for that is a security limitation set by default not allowing httpd servers sur connect a remote DB.
To disable this limitation and make all work, just type in the command line :
# setsebool -P httpd_can_network_connect 1
You can list all the existing flags for httpd by using getsebool
# getsebool -a | grep httpd
In case you expect SELinux to be the cause of your problem, you can enable / disable it with the following functions
# setenforce 1 # setenforce 0
If you need to check what is the permission missing for SELinux you can run the audit
# tail -100 /var/log/audit/audit.log | audit2allow
