systemd: The Good Parts

Even though there is some dissatisfaction with systemd in the sysadmin community, James Nugent, an engineer at Samsung Research, shows why it largely fulfills its primary purposes.

In this talk he takes a tour of the great, and sometimes unappreciated or lesser-known features of systemd. He also explains how it can be paired with Packer and Terraform as a component of self-healing systems, and how it can also be used in a production-grade Consul cluster.

Transcript

1. systemd: The Good Parts
   James Nugent
   Samsung Electronics
   @jen20
   

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7. Fedora 15 May 2011
   openSUSE 12.2 September 2012
   CentOS 7.14.04 April 2014
   Red Hat Enterprise Linux 7.0 June 2014
   SUSE Linux Enterprise Server 12 October 2014
   Debian 8 April 2015
   Ubuntu 15.04 April 2015
   systemd Adop+on
   

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8. Fedora 15 May 2011
   openSUSE 12.2 September 2012
   CentOS 7.14.04 April 2014
   Red Hat Enterprise Linux 7.0 June 2014
   SUSE Linux Enterprise Server 12 October 2014
   Debian 8 April 2015
   Ubuntu 15.04 April 2015
   systemd Adop+on
   

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11. systemd
    

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12. Aspects of systemd
    • System and service manager
    • This is what we’ll focus on today
    • So2ware pla6orm for developing other applica9ons
    • We’ll touch on this too
    • “Glue” between the kernel and user applica9ons
    • Some references at the end
    

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13. Units
    

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14. Units
    

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15. Unit File Paths
    • /lib/systemd/system
    • For package-installed units
    • /etc/systemd/system
    • For Administrator-configured units
    • /run/systemd/system
    • For non-persistent run9me modifica9ons
    

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16. name.type
    

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17. name.type
    consul.service
    

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18. name.type
    ssh.socket
    

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19. Service Units
    

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23. Service Unit Types
    • Simple (default) - for executables which run without
    daemonising - like Consul.
    • Forking - for executables which daemonise themselves
    • Oneshot - usually short-lived programs which run to comple9on
    and terminate
    • No+fy - for executables which will no9fy systemd when they
    are started and available for work.
    • Consul now supports this - more later!
    

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24. Unit Commands
    • systemctl enable consul.service
    • systemctl start consul.service
    • systemctl stop consul.service
    • systemctl restart consul.service
    • systemctl status consul.service
    

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25. systemctl status consul.service
    

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26. systemctl status consul.service
    Unit Name & Descrip9on
    

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27. systemctl status consul.service
    Unit Name & Descrip9on Enabled Status
    

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28. systemctl status consul.service
    Unit Name & Descrip9on Enabled Status
    Up9me
    

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29. systemctl status consul.service
    Unit Name & Descrip9on Enabled Status
    Up9me
    All processes
    

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30. systemctl status consul.service
    Unit Name & Descrip9on Enabled Status
    Up9me
    All processes
    Last 10 log lines
    

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31. “Drop-in” ConfiguraGon
    

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32. “Drop-in” Configura+on
    

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33. “Drop-in” Configura+on
    Per-Service Drop-In
    Configura9on Directory
    

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34. “Drop-in” Configura+on
    Loaded Drop-in
    Configura9on Files
    

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35. systemd-delta
    

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36. Common Bootstrapping PaGern
    • Install so2ware from a generic package
    • apt-get install consul
    • Install bootstrapping script and drop-in configura9on from an
    environment-specific package
    • apt-get install consul-bootstrap-aws
    • apt-get install consul-bootstrap-azure
    

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37. Working Example
    

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38. Target Units
    

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40. consul-online.target
    network-online.target
    consul.service
    multi-user.target
    consul-online.service
    service-that-depends-on-consul.service
    

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44. Socket Units
    

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45. If a service dies, its listening socket stays
    around, not losing a single message. After
    a restart of the crashed service it can
    continue right where it left off. If a service
    is upgraded we can restart the service
    while keeping around its sockets, thus
    ensuring the service is continously
    responsive. Not a single connection is lost
    during the upgrade.
    —Lennart Poettering
    

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46. If a service dies, its listening socket stays
    around, not losing a single message. After
    a restart of the crashed service it can
    continue right where it left off. If a service
    is upgraded we can restart the service
    while keeping around its sockets, thus
    ensuring the service is continously
    responsive. Not a single connection is lost
    during the upgrade.
    

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47. If a service dies, its listening socket stays
    around, not losing a single message. After
    a restart of the crashed service it can
    continue right where it left off. If a service
    is upgraded we can restart the service
    while keeping around its sockets, thus
    ensuring the service is continously
    responsive. Not a single connection is lost
    during the upgrade.
    

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48. Permissions
    

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49. Socket Ac+va+on in Go
    Credit: Vincent Bernat - “IntegraBon of a Go Service with systemd” - 2018
    

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50. Socket Ac+va+on in Go
    Credit: Vincent Bernat - “IntegraBon of a Go Service with systemd” - 2018
    

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51. $ go build 404.go
    $ systemd-socket-activate -l 8000 ./404
    Listening on [::]:8000 as 3
    $ curl '[::1]':8000
    404 page not found
    $ curl '[::1]':8000
    404 page not found
    

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52. Service Unit
    

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53. Socket Unit
    

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54. Graceful Shutdown
    

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55. Timer Units
    

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56. Timer Units
    

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57. This talk only scratches the
    surface of the capabiliGes of
    systemd
    

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58. THANK YOU!
    

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59. References
    • https://freedesktop.org/wiki/Software/systemd/
    • https://github.com/jen20/hashidays-nyc
    • https://github.com/hashicorp/consul/pull/3164
    • https://vincent.bernat.im/en/blog/2018-
    systemd-golang-socket-activation
    

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