[Tarantool-patches] [PATCH] core: don't start example instance in postinstall
Olga Arkhangelskaia
arkholga at tarantool.org
Thu May 28 14:33:37 MSK 2020
Hi Alexander!
Thank you very much for detailed feedback and pointing out the things I
even did not think about.
As I understand (correct me if I am wrong) in 2 cases:
1) Installing a package when previous that was removed but not purged
2) Upgrading the package.
So if package already exists - all postrm, prerm are useless.
The only places we actually can take advantage is preinst and postinst
scripts.
Moreover, when Installing a package that was previously removed, but
not purged [2] preinst scripts will be called from
previous version. So only postinst is left to stop existing example
instance and remove the link.
I am confused with the idea of pushing patch in later versions, because
it is rather surprising behaviour.
So I do not mind the first patch, however we still need to stop running
instances (in case they are still running).
The second thought I have that tracking one-time-actions is actually
good idea and may be useful so far(not only in this case). And confuse
user with disabling example instances (in case when they are enabled
again)every time it is bad idea. So the second patch wins.
I guess I need to test it with full CI?
Moreover, I would write a comment why it is done in such a way (with
links to the diagram). Because I failed to find them when writing the
first version of patch.
27.05.2020 19:02, Alexander Turenko пишет:
> I was wondered why the instance is started automatically and found past
> discussions on this topic, see [1].
>
> I also added some thoughts whether it is right to change this: I think
> so, we should disable the default example instance.
>
> See comments for the patch itself below.
>
> [1]: https://github.com/tarantool/tarantool/issues/4507#issuecomment-634567994
>
> WBR, Alexander Turenko.
>
>> core: don't start example instance in postinstall
> Nit: I would use prefix 'build' here. 'core' is usually about the code
> that resides in src/lib/core.
>
> On Wed, Apr 29, 2020 at 03:20:38PM +0300, Olga Arkhangelskaia wrote:
>> After taratool installation on Debuan/Ubuntu from repo, example instance
>> was automatically started over 3301 port. On the other hand example instance
>> on RHEL/CentOS is started manually. Patch does the same for Debian/Ubuntu.
>>
>> Closes #4507
>>
>> @TarantoolBot document
>> Title: manage example instance after installation
>> After tarantool installation from repos on all distros example instance
>> should be managed manually.
> I verified, where the old behaviour is mentioned in the documentation:
>
> | Depending on the release, during installation Tarantool may start a
> | demonstrative global example.lua instance that listens to the 3301
> | port by default. <...>
> |
> | <...>
> |
> | However, we encourage you to perform the instance startup manually,
> | so you can learn.
>
> Cited from [1] and [2].
>
> [1]: https://www.tarantool.io/en/doc/2.4/getting_started/getting_started_db/#using-a-binary-package
> [2]: https://www.tarantool.io/en/doc/2.4/getting_started/using_binary/
>
> In fact this wording does not contradicts with neither of the
> behaviours. I guess it is better to left the documentation as is for a
> while.
>
>> ---
>> Branch:
>> https://github.com/tarantool/tarantool/tree/gh-4507-disable-start-example-instance
> I would check it on a -full-ci branch just in case. Debian package build
> is changed and we should at least ensure that packages are build.
>
> Hope we'll add such builds to verify each push to a developer branch,
> but now it is only on -full-ci and release branches.
>
>> debian/tarantool-common.postinst | 8 --------
>> 1 file changed, 8 deletions(-)
>>
>> diff --git a/debian/tarantool-common.postinst b/debian/tarantool-common.postinst
>> index e2eda3415..03e4b2215 100644
>> --- a/debian/tarantool-common.postinst
>> +++ b/debian/tarantool-common.postinst
>> @@ -22,14 +22,6 @@ case "$1" in
>> install -d -o$SYSUSER -gadm -m2750 /var/log/tarantool
>> install -d -o$SYSUSER -g$SYSUSER -m750 /var/run/tarantool
>> install -d -o$SYSUSER -g$SYSUSER -m750 /var/lib/tarantool
>> -
>> - # Enable example.lua by default
>> - if [ -z $2 ] && [ ! -e /etc/tarantool/instances.enabled/example.lua ] &&
>> - [ -d /etc/tarantool/instances.enabled ] &&
>> - [ -d /etc/tarantool/instances.available/ ]; then
>> - ln -s /etc/tarantool/instances.available/example.lua \
>> - /etc/tarantool/instances.enabled/example.lua
>> - fi
> /etc/tarantool/instances.enabled/example.lua will not be removed
> automatically even after tarantool-common upgrade, because the symlink
> will be removed in debian/tarantool-common.postrm only at `apt-get purge
> tarantool-common`.
>
> One possible way is to left everything as is and mention necessary steps
> to get rid from example.lua symlink (say, `apt-get purge
> tarantool-common`, `apt-get install tarantool-common`) in release notes.
>
> However it looks as a lie: as user I would expect that the new behaviour
> will become in effect just after upgrade. But we should not remove the
> symlink every time when tarantool-common is updated, because a user may
> want to use this example instance.
>
> I looked over the Debian maintainer scripts documentation ([2], [3]) and
> found several ways to stop and disable an instance on upgrade.
>
> [2]: https://www.debian.org/doc/debian-policy/ch-maintainerscripts.html
> [3]: https://www.debian.org/doc/debian-policy/ap-flowcharts.html
>
> First, we can compare 'previously configured' and 'newly configured'
> versions on 'postinst configure' stage of tarantool-common. This,
> however, both ugly and fragile. It is ugly, because we don't know exact
> four-digits version at which the patch will land into all long-term
> branches: so we'll likely remove the symlink during several upgrades,
> not only one. It is fragile, because it will not be reliable if we'll
> decide to push the patch to, say, 1.10 later (it should be included into
> the condition of the master patch).
>
> It would look like so (not tested):
>
> diff --git a/debian/tarantool-common.postinst b/debian/tarantool-common.postinst
> index 03e4b2215..17d6982c0 100644
> --- a/debian/tarantool-common.postinst
> +++ b/debian/tarantool-common.postinst
> @@ -22,6 +22,13 @@ case "$1" in
> install -d -o$SYSUSER -gadm -m2750 /var/log/tarantool
> install -d -o$SYSUSER -g$SYSUSER -m750 /var/run/tarantool
> install -d -o$SYSUSER -g$SYSUSER -m750 /var/lib/tarantool
> +
> + if [ -e /etc/tarantool/instances.enabled/example.lua ] &&
> + [ -n "$2" ] && (dpkg --compare-versions $2 lt 2.4.2 ||
> + (dpkg --compare-versions $2 gt 2.5.0 &&
> + dpkg --compare-versions $2 lt 2.5.1)); then
> + rm /etc/tarantool/instances.enabled/example.lua
> + fi
> ;;
> esac
>
> Then next way I considered is to add /etc/tarantool/debian/keep
> directory, which will hold files that should be hold during upgrade. But
> it looks weird: there is only one file we want to remove from the old
> configuration during upgrade and unlikely there will be more. This
> mechanism looks artificial here.
>
> So I implemented it in the migration-style way, see the patch below the
> email.
>
> Please, note that enabled instances directory now can be empty and it
> would be good to handle this case in the systemd unit generator file (it
> is in the patch below too).
>
> To be honest, I still don't very like the result (those upgrade markers
> right in /etc), but at least it looks like a general mechanism that may
> be used again (but I hope it will not). If dpkg would provide some
> database for performing migrations during updates, I would use it. But
> it seems, no: it is overkill for dpkg (I don't found anything like
> this).
>
> Olya, Igor, Oleg, can you look into this change and say what do you
> think about?
>
> ----
>
> diff --git a/debian/tarantool-common.postinst b/debian/tarantool-common.postinst
> index 03e4b2215..e368cdd2e 100644
> --- a/debian/tarantool-common.postinst
> +++ b/debian/tarantool-common.postinst
> @@ -22,6 +22,46 @@ case "$1" in
> install -d -o$SYSUSER -gadm -m2750 /var/log/tarantool
> install -d -o$SYSUSER -g$SYSUSER -m750 /var/run/tarantool
> install -d -o$SYSUSER -g$SYSUSER -m750 /var/lib/tarantool
> +
> + # Track configuration updates we want to perform only
> + # once.
> + UPGRADE_DIR="/etc/tarantool/debian/upgrade"
> + mkdir -p "${UPGRADE_DIR}"
> +
> + # Add README file to /etc/tarantool/debian/upgrade
> + # to don't confuse a user with this directory.
> + UPGRADE_FILE_0000="${UPGRADE_DIR}/0000-add-readme.done"
> + if [ ! -e "${UPGRADE_FILE_0000}" ]; then
> + cat << EOF > "${UPGRADE_DIR}/README"
> +There are rare cases, when existing configuration files
> +content or structure should be upgraded when a new package
> +version is installed.
> +
> +This directory tracks performed updates.
> +EOF
> + touch "${UPGRADE_FILE_0000}"
> + fi
> +
> + # Stop and disable example.lua if it was started/enabled,
> + # but do it only once in case a user actually want the
> + # instance be enabled.
> + UPGRADE_FILE_0001="${UPGRADE_DIR}/0001-disable-example-instance.done"
> + if [ ! -e "${UPGRADE_FILE_0001}" ]; then
> + # Stop the instance if it was started.
> + if command -v invoke-rc.d > /dev/null; then
> + invoke-rc.d tarantool at example stop || true
> + else
> + /etc/init.d/tarantool at example stop || true
> + fi
> +
> + # Disable the instance, but keep it in
> + # instances.available.
> + if [ -e /etc/tarantool/instances.enabled/example.lua ]; then
> + rm /etc/tarantool/instances.enabled/example.lua
> + fi
> +
> + touch "${UPGRADE_FILE_0001}"
> + fi
> ;;
> esac
>
> diff --git a/extra/dist/tarantool-generator.in b/extra/dist/tarantool-generator.in
> index f6a6a2540..2048b7517 100755
> --- a/extra/dist/tarantool-generator.in
> +++ b/extra/dist/tarantool-generator.in
> @@ -13,6 +13,7 @@ mkdir -p "$wantdir"
>
> for file in @TARANTOOL_ENABLEDDIR@/*.lua; do
> instance=`basename $file .lua`
> + [ "${instance}" = "*" ] && break # skip empty directory
> ln -s "$service" "$wantdir/tarantool@$instance.service"
> done
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