Attempts to eliminate some systemd unit cyclical dependencies (#181)

* Adjusts ordering and requirements for /cache mounts and formatting if the disk to avoid cyclical dependencies (caused by implicit dependencies). * Makes format-cache.service depend on local-fs-pre.target to be sure that disk devices are available. * Configures format-cache.service to start after dev-sda.device. * Adds Requires=dev-sda.device to format-cache.service. * Removes Requires=dev-sda.device to format-cache.service. * Removes ordering and dependency statements from mounts and moves them all to format-cache.service, since that is the unit that needs to be treated in a non-default way. * Tries relying solely on RequiresMountsFor. * Removes RequiresMountsFor, and readds Before, and adds RequiredBy for various mounts. * Moves RequiredBy to Install section, adds back DefaultDependencies=no. * Adds brief comments about why we add certain dependencies and ordering.
m-lab · Jul 1, 2020 · c2d5e9c · c2d5e9c
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commit c2d5e9c
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diff --git a/configs/stage3_ubuntu/etc/systemd/system/cache-data.mount b/configs/stage3_ubuntu/etc/systemd/system/cache-data.mount
@@ -1,8 +1,5 @@
 [Unit]
 Description=Mount Experiment Data Volume
-Before=docker.service
-After=format-cache.service
-Requires=format-cache.service
 
 [Mount]
 What=/dev/disk/by-label/cache-data

diff --git a/configs/stage3_ubuntu/etc/systemd/system/cache-docker.mount b/configs/stage3_ubuntu/etc/systemd/system/cache-docker.mount
@@ -1,8 +1,5 @@
 [Unit]
 Description=Mount Docker Data Volume
-Before=docker.service
-After=format-cache.service
-Requires=format-cache.service
 
 [Mount]
 What=/dev/disk/by-label/cache-docker

diff --git a/configs/stage3_ubuntu/etc/systemd/system/format-cache.service b/configs/stage3_ubuntu/etc/systemd/system/format-cache.service
@@ -1,9 +1,9 @@
 [Unit]
-Before=docker.service cache-docker.mount cache-data.mount cache-core.mount
-RequiresMountsFor=/cache
-ConditionPathExists=!/cache/docker
+# We want this unit to run before we mount to be sure that disk gets formatted first.
+Before=cache-data.mount cache-docker.mount
 ConditionPathExists=!/cache/data
-ConditionPathExists=!/cache/core
+ConditionPathExists=!/cache/docker
+DefaultDependencies=no
 
 [Service]
 Type=oneshot
@@ -28,5 +28,7 @@ ExecStart=/usr/sbin/mkfs.xfs -f -L cache-data /dev/sda1
 ExecStart=/usr/sbin/mkfs.xfs -f -L cache-docker /dev/sda2
 
 [Install]
+# This requirement should cause these mounts to fail if this unit fails.
+RequiredBy=cache-data.mount cache-docker.mount
 WantedBy=multi-user.target