Articles

Deploying Openstack PoC on CentOS with linux bridge

I was recently in a need to start "playing" with Openstack (working in an existing RDO setup) so I thought that it would be good idea to have my personal playground to start deploying from scratch/breaking/fixing that playground setup.

At first sight, Openstack looks impressive and "over-engineered", as it's complex and have zillions of modules to make it work. But then when you dive into it, you understand that the choice is yours to make it complex or not. Yeah, that sentence can look strange, but I'll explain you why.

First, you should just write your requirements, and then only have a look at the needed openstack components. For my personal playground, I just wanted to have a basic thing that would let me deploy VMs on demand, in the existing network, and so directly using bridge as I want the VMs to be directly integrated into the existing network/subnet.

So just by looking at the mentioned diagram, we just need :

  • keystone (needed for the identity service)
  • nova (hypervisor part)
  • neutron (handling the network part)
  • glance (to store the OS images that will be used to create the VMs)

Now that I have my requirements ...


Remotely kicking a CentOS install through ligthweight 1Mb iso image

As a sysadmin, you probably deploy your bare-metal nodes through kickstarts in combination with pxe/dhcp. That's the most convenient way to deploy nodes in an existing environment. But what about having to remotely init a new DC/environement, without anything at all ? Suppose that you have a standalone node that you have to deploy, but there is no PXE/Dhcp environment configured (yet).

The simple solution would be to , as long as you have at least some kind of management/out-of-band network, to either ask the local DC people to burn the CentOS Minimal iso image on a usb stick, or other media. But I was in a need to deploy a machine without any remote hand available locally there to help me. The only things I had were :

  • access to the ipmi interface of that server
  • the fixed IP/netmask/gateway/dns settings for the NIC connected to that segment/vlan

One simple solution would have been to just "attach" the CentOS 7 iso as a virtual media, and then boot the machine, and setup from "locally emulated" cd-rom drive. But that's not something I wanted to do, as I didn't want to slow the ...


Enabling SPF record for centos.org

In the last weeks, I noticed that spam activity was back, including against centos.org infra. One of the most used technique was Email Spoofing (aka "forged from address"). That's how I discovered that we never implemented SPF for centos.org (while some of the Infra team members had that on their personal SMTP servers).

While SPF itself is "just" a TXT dns record in your zone, you have to think twice before implementing it. And publishing yourself such a policy doesn't mean that your SMTP servers are checking SPF either. There are PROS and CONS to SPF so read first multiple sources/articles to understand how it will impact your server/domain when sending/receiving :

sending

The first thing to consider is how people having an alias can send send their mails : either behind their known MX borders (and included in your SPF) or through alternate SMTP servers relaying (after being authorized of course) through servers listed in your SPF.

One thing to know with SPF is that it breaks plain forwarding and aliases but it's not how you will setup your SPF record, but how originator domain does it : For example if you have joe ...


Music recording on CentOS 7 DAW

There was something that was on my (private) TODO list for quite some time now : being able to record music, mix and output a single song from multiple recorded tracks. For that you need a Digital Audio Workstation DAW.

I have several instruments at home (electric guitars, bass, digital piano and also drums) but due to lack of (free) time I never investigated the DAW part on Linux and especially CentOS. So having some "offline" days during the holidays helped me investigating that and also being able to setup a small DAW on a recycled machine. Let's consider the hardware and software parts.

Hardware support

I personally still own a Line6 TonePort UX2 interface which is now more than 10 years old, and that I used in the past on a iMac. The iMac still runs, but exclusively with CentOS 7 those days, and the TonePort was just collecting dust. When I tried to plug it , it wasn't really detected, but just mainly because of the kernel config, so I asked (gently) Toracat to enable the required kernel module in the centos-plus kernel and with the centos-plus kernel, the toneport ux2 is seen as an external sound card ...


Zabbix, selinux and CentOS 7.3.1611

If you're using CentOS, you probably noticed that we have a CR repository containing all the built packages for the next minor release, so that people can "opt-in" and already use those packages, before they are released with the full installable tree and iso images.

Using those packages on a subset of your nodes can be interesting, as it permits you to catch some errors/issues/conflicts before the official release (and so symlink on mirrors being changed to that new major.minor version)

For example, I tested myself some roles and found an issue with zabbix-agent refusing to start on a node fully updated/rebooted with CR pkgs (so what will become 7.3.1611 release). The issue was due to selinux denying something (that was allowed in previous policy)

Here is what selinux had to say about it :

type=AVC msg=audit(1480001303.440:2626): avc:  denied  { setrlimit } for  pid=22682 comm="zabbix_agentd" scontext=system_u:system_r:zabbix_agent_t:s0 tcontext=system_u:system_r:zabbix_agent_t:s0 tclass=process

It's true that there was an update for selinux policy : from selinux-policy-3.13.1-60.el7_2.9.noarch to selinux-policy-3.13.1-102.el7.noarch.

What's interesting is that I found the ...


(ab)using Alias for Zabbix

It's not a secret that we use Zabbix to monitor the CentOS.org infra. That's even a reason why we (re)build it for some other architectures, including aarch64,ppc64,ppc64le on CBS and also armhfp

There are really cool things in Zabbix, including Low-Level Discovery. With such discovery, you can create items/prototypes/triggers that will be applied "automagically" for each discovered network interface, or mounted filesystem. For example, the default template (if you still use it) has such item prototypes and also graph for each discovered network interface and show you the bandwidth usage on those network interfaces.

But what happens if you suddenly want to for example to create some calculated item on top of those ? Well, the issue is that from one node to the other, interface name can be eth0, or sometimes eth1, and with CentOS 7 things started to also move to the new naming scheme, so you can have something like enp4s0f0. I wanted to create a template that would fit-them-all, so I had a look at calculated item and thought "well, easy : let's have that calculated item use a user macro that would define the name of the interface ...


CentOS Infra public service dashboard

As soon as you're running some IT services, there is one thing that you already know : you'll have downtimes, despite all your efforts to avoid those...

As the old joke says : "What's up ?" asked the Boss. "Hopefully everything !" answered the SysAdmin guy ....

You probably know that the CentOS infra is itself widespread, and subject to quick move too. Recently we had to announce an important DC relocation that impacts some of our crucial and publicly facing services. That one falls in the "scheduled and known outages" category, and can be prepared. For such "downtime" we always announced that through several mediums, like sending a mail to the centos-announce, centos-devel (and in this case , also to the ci-users) mailing lists. But even when we announce that in advance, some people forget about it, or people using (sometimes "indirectly") the concerned service are surprized and then ask about it (usually in #centos or #centos-devel on irc.freenode.net).

In parallel to those "scheduled outages", we have also the worst ones : the unscheduled ones. For those ones, depending on the impact/criticity of the impacted service, and also the estimated RTO, we also send a mail to the concerned mailing ...


Generating multiple certificates with Letsencrypt from a single instance

Recently I was discussing with some people about TLS everywhere, and we then started to discuss about the Letsencrypt initiative. I had to admit that I just tested it some time ago (just for "fun") but I suddenly looked at it from a different angle : while the most used case is when you install/run the letsencrypt client on your node to directly configure it, I have to admit that it's something I didn't want to have to deal with. I still think that proper web server configuration has to happen through cfgmgmt, and not through another process. (and same for the key/cert distribution, something for a different blog post maybe).

If so you're (pushing|pulling) automatically your web servers configuration from $cfgmgmt, but that you want to use/deploy TLS certificates signed by letsencrypt, what can you do ? Well, the good news is that you don't have to be forced to let the letsencrypt client touch your configuration at all : you can use the "certonly" option to just generate the private key locally, send the csr and get the signed cert back (and the whole chain too) One thing to know about letsencrypt is ...


IPv6 connectivity status within the CentOS.org infra

Recently, some people started to ask proper IPv6/AAAA record for some of our public mirror infrastructure, like mirror.centos.org, and also msync.centos.org

Reason is that a lot of people are now using IPv6 wherever possible and from a CentOS point of view, we should ensure that everybody can have content over (legacy) ipv4 and ipv6. Funny that I call ipv4 "legacy" as we still have to admit that it's still the default everywhere, even in 2016 with the available pools now exhausted.

While we had already some AAAA records for some of our public nodes (like www.centos.org as an example), I started to "chase" after proper and native ipv6 connectivity for our nodes. That's where I had to take contact with all our valuable sponsors. First thing to say is that we'd like to thank them all for their support for the CentOS Project over the years : it wouldn't have been possible to deliver multiple terrabytes of data per month without their sponsorship !

WRT ipv6 connectivity that's where the results of my quest where really different : while some DCs support ipv6 natively, and even answer you in 5 minutes ...


Kernel 3.10.0-327 issue on AMD Neo processor

As CentOS 7 (1511) was released, I thought it would be a good idea to update several of my home machines (including kids' workstations) with that version, and also newer kernel. Usually that's just a smooth operation, but sometimes some backported features/new features, especially in the kernel, can lead to some strange issues. That's what happened for my older Thinkpad Edge : That's a cheap/small thinkpad that Lenovo did several years ago ( circa 2011 ), and that I used a lot just when travelling, as it only has a AMD Athlon(tm) II Neo K345 Dual-Core Processor. So basically not a lot of horse power, but still something convenient just to read your mails, remotely connect through ssh, or browse the web. When rebooting on the newer kernel, it panics directly.

Two bug reports are open for this, one on the CentOS Bug tracker, linked also to the upstream one. Current status is that there is no kernel update that will fix this, but there is a easy to implement workaround :

  • boot with the initcall_blacklist=clocksource_done_booting kernel parameter added (or reboot on previous kernel)
  • once booted, add the same parameter at the end of the GRUB_CMDLINE_LINUX=" .." line ...