nixos/postgresqlBackup: Only replace backup when successful

Previously, a failed backup would always overwrite ${db}.sql.gz,
because the bash `>` redirect truncates the file; even if the
backup was going to fail.
On the next run, the ${db}.prev.sql.gz backup would be
overwritten by the bad ${db}.sql.gz.

Now, if the backup fails, the ${db}.in-progress.sql.gz is in an
unknown state, but ${db}.sql.gz will not be written.
On the next run, ${db}.prev.sql.gz (our only good backup) will
not be overwritten because ${db}.sql.gz does not exist.
This commit is contained in:
Robert Hensing 2021-06-04 17:34:26 +02:00
parent c586e42763
commit 81c8189a84
2 changed files with 27 additions and 1 deletions

View file

@ -17,6 +17,8 @@ let
path = [ pkgs.coreutils pkgs.gzip config.services.postgresql.package ];
script = ''
set -e -o pipefail
umask 0077 # ensure backup is only readable by postgres user
if [ -e ${cfg.location}/${db}.sql.gz ]; then
@ -24,7 +26,9 @@ let
fi
${dumpCmd} | \
gzip -c > ${cfg.location}/${db}.sql.gz
gzip -c > ${cfg.location}/${db}.in-progress.sql.gz
mv ${cfg.location}/${db}.in-progress.sql.gz ${cfg.location}/${db}.sql.gz
'';
serviceConfig = {

View file

@ -73,8 +73,30 @@ let
machine.succeed(
"systemctl start ${backupService}.service",
"zcat /var/backup/postgresql/${backupName}.sql.gz | grep '<test>ok</test>'",
"ls -hal /var/backup/postgresql/ >/dev/console",
"stat -c '%a' /var/backup/postgresql/${backupName}.sql.gz | grep 600",
)
with subtest("Backup service fails gracefully"):
# Sabotage the backup process
machine.succeed("rm /run/postgresql/.s.PGSQL.5432")
machine.fail(
"systemctl start ${backupService}.service",
)
machine.succeed(
"ls -hal /var/backup/postgresql/ >/dev/console",
"zcat /var/backup/postgresql/${backupName}.prev.sql.gz | grep '<test>ok</test>'",
"stat /var/backup/postgresql/${backupName}.in-progress.sql.gz",
)
# In a previous version, the second run would overwrite prev.sql.gz,
# so we test a second run as well.
machine.fail(
"systemctl start ${backupService}.service",
)
machine.succeed(
"stat /var/backup/postgresql/${backupName}.in-progress.sql.gz",
"zcat /var/backup/postgresql/${backupName}.prev.sql.gz | grep '<test>ok</test>'",
)
with subtest("Initdb works"):
machine.succeed("sudo -u postgres initdb -D /tmp/testpostgres2")