I'm an experienced software, cloud, and site reliability engineer, and you've found my github profile!

So far I've spent the last 15 years writing software and building infrastructure for startups. I am a strong believer in the power of effective remote work, and the creative and technical benefits of having strong human bonds on technical teams, be they community-driven, open source, or business-oriented.

I recently realized that there was an outage map for one of our utilities. Very interesting. I like playing with data, so I decided to start collect some historical data. A quick inspection of the website showed that there are 2 urls which will happily provide JSON data about current outages, so I set about to collect the data via a once-a-minute kubernetes cron job.

- apiVersion: batch/v1
  kind: CronJob
  metadata:
    name: outages
    namespace: default
  spec:
    concurrencyPolicy: Forbid
    failedJobsHistoryLimit: 1
    jobTemplate:
      metadata:
        name: outages
      spec:
        template:
          spec:
            containers:
            - command:
              - wget
              - -qO-
              - <URL>
              image: busybox
              imagePullPolicy: IfNotPresent
              name: outages
            restartPolicy: OnFailure
    schedule: '*/1 * * * *'
    startingDeadlineSeconds: 10
    successfulJobsHistoryLimit: 3

The Job starts, the output of the wget command is logged, and then it's done. I can pull the relevant log events, and do any kind of analysis on them that I want. This works great, but there are a couple of important elements that are worth remembering. One is the startingDeadlineSeconds. I just wanted to skip the cronjob if it was delayed, instead of "hammering" the service with requests, so I put this at 10 seconds, and I also put concurrencyPolicy: Forbid for the same reason.

The interesting action I observed is with my use of vector as the logging persistence engine in my cluster. It's not complicated, vector just writes logs to files in a particular directory right now, which are periodically mirrored elsewhere. However, I also collect metrics in a variety of ways, and one of them results in output to the same directory. I noticed a consistent increase in the size of the contents of the files in this directory, pre-compression. The backing reason was that vector keeps metrics of every log stream it consumes, and it was recording the tagged log streams of each cron job separately. As a result, each tiny cron job would generate new dimensions for a metric on the vector instance. Due to the quirks of my metric recording system, there would be continued overhead in recording these immobile metrics to storage. I found the solution in a comment on an open issue on the vector github repo. It was there in the docs the whole time! However, it makes me curious about what the real "default behavior" should be, as there are enough comments on that issue to suggest that this is a commonly encountered scenario.

Some years ago, I bought a couple of AP9211 remote power management PDU's. This is effectively a large power strip in a rackmountable box. All of the ports are standard NEMA 5-15 connectors, which is very convenient if you want to plug in some standard sort of gear (say, a fan or something). These came with AP9606 network management cards, so you can turn each socket on or off via the network (in this case, telnet is the most convenient port, but of course these are mostly unsecured, and I wouldn't run one on any sort of network that wasn't just a direct connection to a well-secured machine).

While I know this PDU worked at one point, it had been offline for a while, and was already 20 years old. Unfortunately, when I logged in via telnet, I was met with the following greeting:

Connected to 10.0.2.10.
Escape character is '^]'.

User Name : apc
Password  : ***


American Power Conversion               Web/SNMP Management Card AOS     v3.0.3
(c) Copyright 2000 All Rights Reserved  MasterSwitch APP                 v2.2.0
-------------------------------------------------------------------------------
Name      : Unknown                     Date    : 06/16/2024
Contact   : Unknown                     Time    : 13:50:52
Location  : Unknown                     Up Time : 0 Days 0 Hours 15 Minutes
Status    : P+ N+ A-                    User    : Administrator


------- Control Console -------------------------------------------------------

     1- Device Manager
     2- Network
     3- System
     4- Logout

     <ESC>- Main Menu, <ENTER>- Refresh

That's right, the Status: line containing A- indicated that the application, which is the bit that actually manages the ports (the whole point of this component) was not properly loaded. Amazingly, I don't believe the time there was set by NTP, so this device must be properly holding the time 20 years post-manufacture! Anyway, the lack of management firmware availability was confirmed when I tried to navigate to the Device Manager, and was greeted with an empty menu. When operating normally, the device manager should give the option to configure the ports in a variety of ways. Also, connecting via the rudimentary FTP server only showed the 303 firmware for the management card. So, what now?

Despite the relatively ancient provenance of this card (the copyright on the removable APC AP9606 management board is 1998, but the firmware claims the maufacture date is 2000 ), I found some firmware blobs which had been reported working in a forum[1]. I attempted an upgrade, but, unfortunately, it failed. Of course, that meant I had a good reason to open the unit! Inside, the board is a simple one-sided PCB, with one relay per switch, and a standard looking ribbon cable connecting to the management card. I dug in and was able to find some resources on pinouts, but I also realized that a replacement management card is $10 on ebay, so I'll be ordering one of those to test. More to come later!

How do I enable/disable autologin for a tty?

If you're using a linux machine, you are likely using either systemd, or possibly rc-init. Some systems enable autologin in a specific TTY, or allow configuration to do so. A good example in Flatcar Linux. If deploying to baremetal, or experimenting in a VM, there may be some scenarios where you want to be able to administer the system in the short term without configuring SSH up front, or even enabling networking.

Another scenario might be persistent VM infrastructure on a laptop. Usually your primary OS will be protected by authentication, with encrypted partitions, etc. In this scenario, enabling authentication on an internal VM is likely overkill from a security perspective, and can be an annoying unnecessary step in your workflow.

It's possible to enable autologin with agetty using the -a <username> flag, or with login with login -f <username>. Of course, things like gdm also have pam module configurations to enable login-by-default.

I would expect most user-facing linux systems today (except android) to utilize systemd, in which case you probably have the getty@ service, which can be edited with systemctl edit [email protected] for any tty, or for a specific tty by putting it after the @ sign (ie, systemctl edit [email protected]. This doesn't edit the underlying file, but instead is a helper method for generating override.conf files in /etc/systemd/system. After editing the file, it will be necessary to call systemctl daemon-reload and restart the service.

The specific use case that triggered this FAQ was specifying autologin in the command line for a particular flatcar linux system booted over ipxe. Out of caution/paranoia, I wanted to disable login after setting up (manually, unfortunately) the network on the system. The override file I generated looks like this, and after doing the reload dance, the terminal was no longer automatically logging in:

#/etc/systemd/system/getty\@tty1.service.d/override.conf 
ExecStart=
ExecStart=-/sbin/agetty --noclear %I $TERM

I do have some non-systemd systems, and when login is managed by rc-init, the tty login behavior will likely be managed in the file /etc/inittab. Here is an exaple of agetty managing the second tty2 for console 2:

c2:2345:respawn:/sbin/agetty 38400 tty2 linux

To test modifying this behavior, change the file and issue the telinit q command. Then switch to the console (ctrl+alt+f2 for me), and you will see the change (autologin or whatever).

One useful application of this is USB serial device access to a system with problematic networking, which I hope to follow up on in a subsequent FAQ.

Recently I upgraded a machine from Ubuntu release 20.04 to release 22.04. This install was migrated to this laptop, where it lives alongsied another Ubuntu 22.04 release. The core reason (in addition to receiving better regular updates,i) was some stuttering that I experienced on google meet calls. It seemed less prevalent on zoom, but who knows if that was accurate, or just luck of the draw. In the end I switched several things to try to get up to date on my Thinkpad P1 Gen3 laptop.

First, and the biggest surprise: despite having run through a do-release-upgrade, I was still on a 5.15 kernel! I had to uninstall the old hardware enablement package and install the new kernel 6.5 hardware enablement package.

Second, adding proprietary NVIDIA drivers. The nouveau driver seems to be better on the 6.X line of kernels, but I was still experiencing occasional artifacts. The NVIDIA drivers seem to have resolved that, but this laptop also has an intel graphics card for when battery life is more important than performance. I need to verify that the appropriate graphics card is being utilized properly, when I was checking the resources in use, it seems that there are two possible acceleration APIs, VDPAU and VA-API.

I will test drive this setup for a few meetings (video calls seem to be the only things that suffer, and primarily when I am sharing video). However, if I don't see improvements, I may need to consider switching to an alternative device specifically for these sorts of video calls.

How do I enable TLS on my k3s cluster without certmanager?

CertManager is a great utility, but it's not necessary to install it to get letsencrypt certificates in k3s. Traefik, which provides ingress capabilities for k3s, is perfectly capable of negotiating acme for certificates for you. Additional configuration can be provided to k3s by dropping the following in your installation (with your own email):

$ cat /var/lib/rancher/k3s/server/manifests/traefik-config.yaml
apiVersion: helm.cattle.io/v1
kind: HelmChartConfig
metadata:
  name: traefik
  namespace: kube-system
spec:
  valuesContent: |-
    logs:
      access:
        enabled: true
    certResolvers:
      letsencrypt:
        email: "$(certificate email)"
        caServer: https://acme-v02.api.letsencrypt.org/directory # Production server
        tlsChallenge: true

Then, using the defined certResolver on traefik ingresses (be sure to specify both FQDNs!):

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: grafana
  namespace: monitoring
  annotations:
    traefik.ingress.kubernetes.io/router.entrypoints: websecure
    traefik.ingress.kubernetes.io/router.tls.certresolver: letsencrypt
    traefik.ingress.kubernetes.io/router.tls.domains.0.main: $(your fqdn)
spec:
  rules:
  - host: $(your fqdn)
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: prometheus-k8s
            port:
              number: 9090

Note the certresolver in the ingress annotation is a reference to the certresolver defined in the HelmChartConfig (the token being letsencrypt in this case).

Also, notice that this enables access logs for the traefik proxies.

Is this easier than installing CertManager? Not sure, but it's definitely one less moving piece if you don't need fullblown certificate management, but just want to expose a few websites.

How do I set the hostname of a system fom the kernel command line?

Recently, I was using qemu to run some VMs, which were connected directly to IPv4, with no dhcp in place. It is possible to configure the network information via a parameter that is set on the kernel command line. Usually if you're using linux, the kernel command line is set by your bootloader, likely GRUB. In my case, I was using QEMU to run the kernel directly, which allows the specification of the command like via a kernel argument, something like this:

qemu-system-x86_64 -machine accel=kvm -cpu host,vmx=on -m 12G -smp 2 -kernel flatcar_production_image.vmlinuz -initrd flatcar_production_pxe_image.cpio.gz -append flatcar.autologin=ttyS0 console=ttyS0 ip=192.168.0148::192.168.0145:255.255.255.0:k3s:eth0:none:1.1.1.1 rootfstype=btrfs sshkey="'"$(cat .ssh/id_rsa.pub)"'"' -nographic

I was slightly surprised that the resulting system was using 'localhost' as a hostname, when the client hostname is specified as a parameter in the network configuration:

ip=192.168.0148::192.168.0145:255.255.255.0:k3s:eth0:none:1.1.1.1

I went digging and found that the only hostname systemd will extract from the commandline is one specified with systemd.hostname, like systemd.hostname=k3s. An easy addition, but I think that adding the possibility to utilize the hostname set in the ip argument might be interesting as a fallback. Of course there is always the possibility for surprising resullts for people with different usecases, so it's worth considering such a change very thoughtfully.

How do I boot QEMU to test an IPXE setup?

I like to build an EFI usb, and test via this command:

qemu-system-x86_64 -machine accel=kvm -bios bin-x86_64-efi/OVMF_CODE.fd -hda bin-x86_64-efi/ipxe.usb -monitor stdio -m 4g