Hi Evans, I am late in answering as well :)
I thought about it and I think that with the right premises (example: this is tailored for Wikimedia's environment, it assumes that a cluster downtime is acceptable, etc..) the storytelling style might be more easy to digest than a list of steps to follow. I think that in all use cases different from Wikimedia there will be adjustments to make, and things that work/don't-work/etc.. One thing that it might be good to add at the end is a "summary of known pitfalls/bugs/etc.." found during the procedure, that in my case were the most time-consuming ones. I'll add it during the next few days and people can comment :) The Blog post would be a good idea, maybe something that we can share between Wikimedia and Apache? I am planning to move to BigTop during the upcoming quarter (October -> December), that will also show if my procedure works on a cluster of 60+ nodes (rather than on a small one of 8 nodes) :D. As soon as I have done it I'll follow up with this list so organize a blog post, does it sound ok? Thanks a lot for all the support! Luca On Tue, Sep 15, 2020 at 6:06 PM Evans Ye <evan...@apache.org> wrote: > > Hey Luca, > > Sorry for the late reply. I was busy for a conference. It's just over now. > Anyway, I think the writing is pretty informative. But it's more like a > storytelling style. Also several contents are WikiMedia specific things. > That's why I think it's more suitable for a blogpost. > > Anyhow, I think either way it's great content. If we keep it as is, I think > we can make it available on Bigtop's WIKI & Blog, or even Success at Apache > with the title like "WikiMedia's story to migrate from CDH to Bigtop". If you > want to make it more like an official guide, the title will be "CDH to Bigtop > Migration Guide". We can state the limitation and environment so that people > can take it w/ a caution that it might not suit their own environment. > > Which way to go depends on how much effort you'd like to take. Let me know > what you think so that we can move forward. > > - Evans > > Luca Toscano <toscano.l...@gmail.com> 於 2020年9月7日 週一 下午3:39寫道： >> >> Hi Evans, >> >> thanks for the review! What are the things that you'd like to see to >> make them more consumable for users? I can re-shape the writing, I >> tried to come up with something to kick off a conversation with the >> community, it would be interesting to know if anybody else has a >> similar use case and how/if they are working on a solution. >> >> For the blogpost, maybe we can coordinate something shared between >> Apache and Wikimedia when the migration is done, I am sure it would be >> a nice example of the two Foundations collaborating :) >> >> Luca >> >> On Wed, Sep 2, 2020 at 8:21 PM Evans Ye <evan...@apache.org> wrote: >> > >> > Hi Luca, >> > >> > I read through the doc briefly. I think the doc works very well as a >> > blogpost of a successful story for Wikimedia migrating from CDH to Bigtop. >> > However, the current writing doesn't seem to be easily consumable for >> > users' who are just looking into the solutions/steps for doing similar >> > migrations. May I know what title you would prefer if we put the doc in >> > Bigtop's wiki? >> > >> > What I was thinking is the cookbook for migration. But we can discuss >> > this. IMHO a Success at Apache[1] blogpost is also possible. But I need to >> > figure out who to talk to. Let me know what you think. >> > >> > [1] https://blogs.apache.org/foundation/category/SuccessAtApache >> > >> > Evans >> > >> > Evans Ye <evan...@apache.org> 於 2020年8月30日 週日 上午3:18寫道： >> >> >> >> Hi Luca, >> >> >> >> I'm on vacation hence do not have time for review right now. I'll get >> >> back to you next week. >> >> >> >> The doc is definitely valuable. Once you have your production migrated >> >> successfully. We can prove to the other users that this is a battle >> >> proven solution. Even more, we can give a talk at ApacheCon or somewhere >> >> else to further amplify the impact of the work. This is definitely an >> >> open source winning case so I think it deserve a talk. >> >> >> >> Evans >> >> >> >> >> >> Luca Toscano <toscano.l...@gmail.com> 於 2020年8月27日 週四 下午9:11寫道： >> >>> >> >>> Hi Evans, >> >>> >> >>> it took a while I know but I have the first version of the gdoc for the >> >>> upgrade: >> >>> >> >>> https://docs.google.com/document/d/1fI1mvbR1mFLV6ohU5cIEnU5hFvEE7EWnKYWOkF55jtE/edit?usp=sharing >> >>> >> >>> I tried to list all the steps involved in migrating from CDH 5 to >> >>> Bigtop 1.4, anybody interested should be able to comment. The idea >> >>> that I have is to discuss this for a few days and then possibly make >> >>> it permanent somewhere in the Bigtop wiki? (of course if the document >> >>> will be considered useful for others etc..) >> >>> >> >>> During these days I tested the procedure multiple times, and I have >> >>> also tested the HDFS finalize step, everything works as expected. I >> >>> hope to be able to move to Bigtop during the next couple of months. >> >>> >> >>> Luca >> >>> >> >>> On Tue, Jul 21, 2020 at 4:04 PM Evans Ye <evan...@apache.org> wrote: >> >>> > >> >>> > Yes. I think a shared gdoc is prefered, and you can open up a JIRA >> >>> > ticket to track it. >> >>> > >> >>> > Luca Toscano <toscano.l...@gmail.com> 於 2020年7月20日 週一 21:10 寫道： >> >>> >> >> >>> >> Hi Evans! >> >>> >> >> >>> >> What is the best medium to use for the documentation/comments ? A >> >>> >> shared gdoc or something similar? >> >>> >> >> >>> >> Luca >> >>> >> >> >>> >> On Thu, Jul 16, 2020 at 5:11 PM Evans Ye <evan...@apache.org> wrote: >> >>> >> > >> >>> >> > One thing I think would be great to have is a doc version of the >> >>> >> > steps for upgrade and rollback. The benefits: >> >>> >> > 1. Anything unexpected happened during automation, you do have >> >>> >> > folks can quickly understand what's going on and get into the >> >>> >> > investigation. >> >>> >> > 2. Share the doc with us to help the others OSS users for doing the >> >>> >> > migration. For the env specific things I think that's fine. We can >> >>> >> > left comment on it. At least all the other users can get a high >> >>> >> > level view of a proven solution. And then they can go and find out >> >>> >> > the rest of the pieces by themselves. >> >>> >> > >> >>> >> > For automations, I suggest to split up the automation into several >> >>> >> > stages, and apply some validation steps(manually is ok) before >> >>> >> > kicking of the next stage. >> >>> >> > >> >>> >> > Best, >> >>> >> > Evans >> >>> >> > >> >>> >> > >> >>> >> > >> >>> >> > >> >>> >> > Luca Toscano <toscano.l...@gmail.com> 於 2020年7月15日 週三 下午9:07寫道： >> >>> >> >> >> >>> >> >> Hi everybody, >> >>> >> >> >> >>> >> >> I didn't get the time to work on this until recently, but I finally >> >>> >> >> managed to have a reliable procedure to upgrade from CDH to Bigtop >> >>> >> >> 1.4 >> >>> >> >> and rollback if needed. The assumptions are: >> >>> >> >> >> >>> >> >> 1) It is ok to have (limited) cluster downtime. >> >>> >> >> 2) Rolling upgrade is not needed. >> >>> >> >> 3) QJM is used. >> >>> >> >> >> >>> >> >> The procedure is listed in these two scripts: >> >>> >> >> >> >>> >> >> https://github.com/wikimedia/operations-cookbooks/blob/master/cookbooks/sre/hadoop/stop-cluster.py >> >>> >> >> https://github.com/wikimedia/operations-cookbooks/blob/master/cookbooks/sre/hadoop/change-distro-from-cdh.py >> >>> >> >> >> >>> >> >> The code is highly dependent on my working environment, but it >> >>> >> >> should >> >>> >> >> be clear to follow when writing a tutorial about how to migrate >> >>> >> >> from >> >>> >> >> CDH to Bigtop. All the suggestions given by this mailing list were >> >>> >> >> really useful to reach a solution! >> >>> >> >> >> >>> >> >> My next steps will be: >> >>> >> >> >> >>> >> >> 1) Keep testing Bigtop 1.4 (finalize HDFS upgrade, run more hadoop >> >>> >> >> jobs, test Hive 2, etc..). >> >>> >> >> 2) Upgrade the production Hadoop cluster to Bigtop 1.4 on Debian 9 >> >>> >> >> (HDFS 2.6.0-cdh -> 2.8.5). >> >>> >> >> 3) Upgrade to Bigtop 1.5 on Debian 9 (HDFS 2.8.5 -> 2.10). >> >>> >> >> 4) Upgrade to Debian 10. >> >>> >> >> >> >>> >> >> With automation it shouldn't be very difficult, I'll report >> >>> >> >> progress once made. >> >>> >> >> >> >>> >> >> Thanks a lot! >> >>> >> >> >> >>> >> >> Luca >> >>> >> >> >> >>> >> >> On Mon, Apr 13, 2020 at 9:25 AM Luca Toscano >> >>> >> >> <toscano.l...@gmail.com> wrote: >> >>> >> >> > >> >>> >> >> > Hi Evans, >> >>> >> >> > >> >>> >> >> > thanks a lot for the feedback, it was exactly what I needed. The >> >>> >> >> > simpler the better is definitely a good advice in this use case, >> >>> >> >> > I'll >> >>> >> >> > try this week another rollout/rollback and report back :) >> >>> >> >> > >> >>> >> >> > Luca >> >>> >> >> > >> >>> >> >> > On Thu, Apr 9, 2020 at 8:09 PM Evans Ye <evan...@apache.org> >> >>> >> >> > wrote: >> >>> >> >> > > >> >>> >> >> > > Hi Luca, >> >>> >> >> > > >> >>> >> >> > > Thanks for reporting back and let us know how it goes. >> >>> >> >> > > I don't have the exactly HDFS with QJM HA upgrade experience. >> >>> >> >> > > The experience I had was 0.20 non-HA upgrade to 2.0 non-HA and >> >>> >> >> > > then enable QJM HA, which was back in 2014. >> >>> >> >> > > >> >>> >> >> > > Regarding to rollback, I think you're right: >> >>> >> >> > > >> >>> >> >> > > it is possible to rollback to HDFS’ state before the upgrade >> >>> >> >> > > in case of unexpected problems. >> >>> >> >> > > >> >>> >> >> > > My previous experience is the same that the rollback is merely >> >>> >> >> > > a snapshot before the upgrade. If you've gone far, then >> >>> >> >> > > rollback cost more data lost... Our runbook is if our sanity >> >>> >> >> > > check failed during upgrade downtime, we perform the rollback >> >>> >> >> > > immediately. >> >>> >> >> > > >> >>> >> >> > > Regarding to that FSImage hole issue, I've experienced it as >> >>> >> >> > > well. >> >>> >> >> > > I managed to fix it by manually edit the FSImage with offline >> >>> >> >> > > image viewer[1] and delete that missing editLog in FSImage. >> >>> >> >> > > That actually brought my cluster back with a little number of >> >>> >> >> > > missing blocks. >> >>> >> >> > > >> >>> >> >> > > Our experience says that the more the steps, the more the >> >>> >> >> > > chance you failed the upgrade. We did good on dozen times of >> >>> >> >> > > testing, DEV cluster, STAGING cluster, but still got missing >> >>> >> >> > > blocks when upgrading Production... >> >>> >> >> > > >> >>> >> >> > > The suggestion is to get your production in good shape >> >>> >> >> > > first(the less decommissioned, offline DNs, disk failures, the >> >>> >> >> > > better). >> >>> >> >> > > Also, maybe you can switch to non-HA mode and do the upgrade >> >>> >> >> > > to simplify the things? >> >>> >> >> > > >> >>> >> >> > > Not many helps but please let us know if any progress. >> >>> >> >> > > Last one, have you reached out to Hadoop community? the >> >>> >> >> > > authors should know the most :) >> >>> >> >> > > >> >>> >> >> > > - Evans >> >>> >> >> > > >> >>> >> >> > > [1] >> >>> >> >> > > https://hadoop.apache.org/docs/r2.8.5/hadoop-project-dist/hadoop-hdfs/HdfsImageViewer.html >> >>> >> >> > > >> >>> >> >> > > Luca Toscano <toscano.l...@gmail.com> 於 2020年4月8日 週三 21:03 寫道： >> >>> >> >> > >> >> >>> >> >> > >> Hi everybody, >> >>> >> >> > >> >> >>> >> >> > >> most of the bugs/issues/etc.. that I found while upgrading >> >>> >> >> > >> from CDH 5 >> >>> >> >> > >> to BigTop 1.4 are fixed, I am now testing (as suggested also >> >>> >> >> > >> in here) >> >>> >> >> > >> upgrade/rollback procedures for HDFS (all written in >> >>> >> >> > >> https://phabricator.wikimedia.org/T244499, will add >> >>> >> >> > >> documentation >> >>> >> >> > >> about this at the end I promise). >> >>> >> >> > >> >> >>> >> >> > >> I initially followed [1][2] in my Test cluster, choosing the >> >>> >> >> > >> Rolling >> >>> >> >> > >> upgrade, but when I tried to rollback (after days since the >> >>> >> >> > >> initial >> >>> >> >> > >> upgrade) I ended up in an inconsistent state and I wasn't >> >>> >> >> > >> able to >> >>> >> >> > >> recover the previous HDFS state. I didn't save the exact error >> >>> >> >> > >> messages but the situation was more or less the following: >> >>> >> >> > >> >> >>> >> >> > >> FS-Image-rollback (created at the time of the upgrade) - up >> >>> >> >> > >> to transaction X >> >>> >> >> > >> FS-Image-current - up to transaction Y, with Y = X + 10000 >> >>> >> >> > >> (number >> >>> >> >> > >> totally made up for the example) >> >>> >> >> > >> QJM cluster: first available transaction Z = X + 10000 + 1 >> >>> >> >> > >> >> >>> >> >> > >> When I tried to rolling rollback, the Namenode complained >> >>> >> >> > >> about a hole >> >>> >> >> > >> in the transaction log, namely at X + 1, so it refused to >> >>> >> >> > >> start. I >> >>> >> >> > >> tried to force a regular rollback, but the Namenode refused >> >>> >> >> > >> again >> >>> >> >> > >> saying that there was no available FS Image to roll back to. >> >>> >> >> > >> I checked >> >>> >> >> > >> in the Hadoop code and indeed the Namenode saves the fs image >> >>> >> >> > >> with >> >>> >> >> > >> different naming/path in case of a rolling upgrade or a >> >>> >> >> > >> regular >> >>> >> >> > >> upgrade. Both cases make sense, especially the first one >> >>> >> >> > >> since there >> >>> >> >> > >> was indeed a hole between the last transaction of the >> >>> >> >> > >> FS-Image-rollback and the first available transaction to >> >>> >> >> > >> reply on the >> >>> >> >> > >> QJM cluster. I chose the rolling upgrade initially since it >> >>> >> >> > >> was >> >>> >> >> > >> appealing: it promises to bring back the Namenodes to their >> >>> >> >> > >> previous >> >>> >> >> > >> versions, but keeping the data modified between upgrade and >> >>> >> >> > >> rollback. >> >>> >> >> > >> >> >>> >> >> > >> I then found [3], in which it is said that with QJM >> >>> >> >> > >> everything is more >> >>> >> >> > >> complicated, and a regular rollback is the only option >> >>> >> >> > >> available. What >> >>> >> >> > >> I think this mean is that due to the Edit log spread among >> >>> >> >> > >> multiple >> >>> >> >> > >> nodes, a rollback that keeps data between upgrade and >> >>> >> >> > >> rollback is not >> >>> >> >> > >> available, so worst case scenario the data modified during >> >>> >> >> > >> that >> >>> >> >> > >> timeframe is lost. Not a big deal in my case, but I want to >> >>> >> >> > >> triple >> >>> >> >> > >> check with you if this is the correct interpretation or if >> >>> >> >> > >> there is >> >>> >> >> > >> another tutorial/guide/etc.. that I haven't read with a >> >>> >> >> > >> different >> >>> >> >> > >> procedure :) >> >>> >> >> > >> >> >>> >> >> > >> Is my interpretation correct? If not, is there anybody with >> >>> >> >> > >> experience >> >>> >> >> > >> in HDFS upgrades that could shed some light on the subject? >> >>> >> >> > >> >> >>> >> >> > >> Thanks in advance! >> >>> >> >> > >> >> >>> >> >> > >> Luca >> >>> >> >> > >> >> >>> >> >> > >> >> >>> >> >> > >> >> >>> >> >> > >> [1] >> >>> >> >> > >> https://hadoop.apache.org/docs/r2.8.5/hadoop-project-dist/hadoop-hdfs/HdfsUserGuide.html#Upgrade_and_Rollback >> >>> >> >> > >> [2] >> >>> >> >> > >> https://hadoop.apache.org/docs/r2.8.5/hadoop-project-dist/hadoop-hdfs/HdfsRollingUpgrade.html >> >>> >> >> > >> [3] >> >>> >> >> > >> https://hadoop.apache.org/docs/r2.8.5/hadoop-project-dist/hadoop-hdfs/HDFSHighAvailabilityWithQJM.html#HDFS_UpgradeFinalizationRollback_with_HA_Enabled
