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
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
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
11. systemd
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
13. Units
14. Units
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
16. name.type
17. name.type consul.service
18. name.type ssh.socket
19. Service Units
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!
24. Unit Commands • systemctl enable consul.service • systemctl start consul.service • systemctl stop consul.service • systemctl restart consul.service • systemctl status consul.service
25. systemctl status consul.service
26. systemctl status consul.service Unit Name & Descrip9on
27. systemctl status consul.service Unit Name & Descrip9on Enabled Status
28. systemctl status consul.service Unit Name & Descrip9on Enabled Status Up9me
29. systemctl status consul.service Unit Name & Descrip9on Enabled Status Up9me All processes
30. systemctl status consul.service Unit Name & Descrip9on Enabled Status Up9me All processes Last 10 log lines
31. “Drop-in” ConfiguraGon
32. “Drop-in” Configura+on
33. “Drop-in” Configura+on Per-Service Drop-In Configura9on Directory
34. “Drop-in” Configura+on Loaded Drop-in Configura9on Files
35. systemd-delta
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
37. Working Example
38. Target Units
40. consul-online.target network-online.target consul.service multi-user.target consul-online.service service-that-depends-on-consul.service
44. Socket Units
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
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.
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.
48. Permissions
49. Socket Ac+va+on in Go Credit: Vincent Bernat - “IntegraBon of a Go Service with systemd” - 2018
50. Socket Ac+va+on in Go Credit: Vincent Bernat - “IntegraBon of a Go Service with systemd” - 2018
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
52. Service Unit
53. Socket Unit
54. Graceful Shutdown
55. Timer Units
56. Timer Units
57. This talk only scratches the surface of the capabiliGes of systemd
58. THANK YOU!
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