Yes. Overall it sounds great to me! I think the "summary of known pitfalls/bugs/etc.." section is worth to add and might be a super valuable part of the whole thing.
| "The Blog post would be a good idea, maybe something that we can share between Wikimedia and Apache" What do you mean by this one, specifically? Currently 3 things we can in below. Do they match what you think or it's something else? 1. Bigtop wiki/blogs: https://cwiki.apache.org/confluence/display/BIGTOP/Index https://blogs.apache.org/bigtop/ 2. Success At Apache: https://blogs.apache.org/foundation/category/SuccessAtApache 3. ApacheCon Talk (this year CFP is over, we can do it next year as a post production expereince sharing) https://apachecon.com/index.html - Evans Luca Toscano <[email protected]> 於 2020年9月20日 週日 下午4:55寫道： > 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 <[email protected]> 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 <[email protected]> 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 <[email protected]> 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 <[email protected]> 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 <[email protected]> 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 <[email protected]> > wrote: > >> >>> > > >> >>> > Yes. I think a shared gdoc is prefered, and you can open up a > JIRA ticket to track it. > >> >>> > > >> >>> > Luca Toscano <[email protected]> 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 <[email protected]> > 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 <[email protected]> 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 < > [email protected]> 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 <[email protected]> > 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 <[email protected]> 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 >
