5 ms·

How does the architecture block major refactors or improvements? Are you running a single codebase for all your tenants, albeit with separate schemas for each?

by gomox 6y ago

How does the architecture block major refactors or improvements? Are you running a single codebase for all your tenants, albeit with separate schemas for each? Edit: on reading the link you included, it seems like a lot of the problems are on the Rails implementation of the architecture with ActiveRecord and Apartment rather than with the architecture itself.

sky_rw 6y ago
For me it falls into the category of decisions that are easy to make and difficult to un-make. If for whatever reason you decide this was the wrong choice for you, be in tech needs (e.g. rails) or business needs, merging your data and going back into a codebase to add this level of filtering is a massive undertaking.
- gomox 6y ago
  Indeed, but if you are making a B2B enterprise/SMB SaaS, I think you are most likely to regret the opposite choice [1][2]. A lot of companies run a single instance, multitenant application and have to develop custom sharding functionality down the road when they realize the inevitable: that most joins and caches are only needed on strict subsets of the data that are tenant specific. If you get successful enough in this type of application space, you reach a mature state in which you need to be able to: * Run large dedicated instances for your largest customers, because either their performance or security requirements mandate it. * Share resources among a large number of smaller customers, for efficiency and fault tolerance reasons. You can get there in two ways: * You start with a massive multi tenant application, and you figure out a way to shard it and separate in pieces later. * You start with multiple small applications, and you develop the ability to orchestrate the group, and scale the largest of them. I would argue the latter is more flexible and cost efficient, and requires less technical prowess. [1] https://news.ycombinator.com/item?id=23307172 https://news.ycombinator.com/item?id=23307172 [2] https://news.ycombinator.com/item?id=23307139 https://news.ycombinator.com/item?id=23307139
  - cornishpixels 6y ago
    You can always take a multi-tenant system and convert it into a single-tenant system a lot more easily. First and foremost, you can simply run the full multi-tenant system with only a single tenant, which if nothing else enables progressive development (you can slowly remove those now-unnecessary WHERE clauses, etc).
    - gomox 6y ago
      True, but: In my experience by the time you reach this point you have a lot of operational complexity because you and your team are used to your production cluster being a single behemoth, so chances are it's not easy to stand up a new one or the overhead for doing so is massive (i.e. your production system grew very complex because there is rarely if ever a need to stand up a new one). Additionally, a multi tenant behemoth might be full of assumptions that it's the only system in town therefore making it hard to run a separate instance (i.e. uniqueness constraints on names, IDs, etc).
      - egamirorrim 6y ago
        Some of the issues I see in one of my projects is high interactivity between accounts. E.g. if account 1 'sends' something to account 2 both of the shared/separate db instances need to be up or there'll need to be some kind of queueing mechanism. That's hard enough and then add to it that most clients want to BYOK to those instances
        gomox 6y ago
        High interactivity between accounts is a good reason to not adopt the proposed multi-single-tenant architecture. The scenarios discussed are B2B enterprisey apps in which the environments are essentially independent from each other.
    - krainboltgreene 6y ago
      > You can always take a multi-tenant system and convert it into a single-tenant system a lot more easily. This is not true if your primary keys are int or bigint. It's also not true if you have any sort of unique indexes that are scoped to a table.
krainboltgreene 6y ago
Here I'll give you one: If you want to change a property of the database that will give your specific use improved performance, you have no way to transactionally apply that change. Rolling back becomes a problem of operational scale, rolling out as well. What if you need to release some feature, but that feature requires a database feature enabled? Normally you enable it once, in a transaction hopefully, and then roll out your application. With this style you have to wait for N database servers to connect, enable, validate, then go live before you can even attempt the application being deployed, much less if you get it wrong.
- lonelappde 6y ago
  You roll the feature out incrementally to the users who are ready. You build backwards compatible features. Basic software engineering.
  - sah2ed 6y ago
    > You roll the feature out incrementally to the users who are ready. You build backwards compatible features. Basic software engineering. The parent mentioned having to support ~150 B2B customers, so the effort is amplified x100 — more than 100 individual customers databases have to be coddled as you’ve described, albeit they are stuck with poor tooling to manage changes across their unusual architecture.
    - magicalhippo 6y ago
      While not a web-app, we too have ~200 B2B customers running our application and each one have their own DB. Some self-host, most others are hosted by us. We have written our own tool to upgrade the DB schema, it's nothing fancy, just takes an XML description, compares with the current DB and makes changes. However it ensures the upgrade process is automated. New versions of our application come with a new DB schema, and we also have an auto-updater for our software. We have a small launcher application which allows the users to select a few older versions of our software, so upgrades are almost always safe in the sense that if the user encounters a bug with the new version, they can try in the previous one. If the DB schema upgrade tool fails for some reason, the application upgrade will be held back and we'll get a notification. Combined this allows us to be quite aggressive with pushing out new versions, and to do so without manual intervention. A limitation with this setup is that DB changes have to be backwards compatible. So we do have a few cases of "if this table exists do this, else do that" type logic and similar, but mostly it's not a big deal. For example I recently had to refactor some old table where they had used five columns for some additional references (ref_1, ref_2 etc), into a new table of additional references. To handle this I just made a new view which would return either the refs from the new table, or the data from the columns in case the new table didn't have any data for that record. I then changed the application to use a grid instead of five separate edit controls, and to use this new view. If the user had to use an older version, that version would just write to the five fields and not populate a row in the new table, and the view would then return this data if the user later viewed it in the new version of our application. So the "overhead" of backwards compatibility in this case was just ensuring this would be sufficient and writing that view, so just a few minutes.

ehsanu1 6y ago
I think you are talking about problems going from multiple single-tenant systems to a single multi-tenant system. You parent is talking about the opposite.
- gomox 6y ago
  No. For example, HubSpot runs a multitenant system. URLs look like: https://app.hubspot.com/section/$ACCOUNT_ID/etc/etc https://app.hubspot.com/section/$ACCOUNT_ID/etc/etc In the simple, YAGNI implementation of this, when you create a new HubSpot account, most likely that will insert a new row into the accounts table, and the auto generated ID of that row will be your account ID. Therefore you need uniqueness to be enforced at that level. If you want to start running a separate copy of the system, you need to refactor the system to move that sequence out of the database so that two different customers running on different clusters don't end up with the same account ID. This is just an example, but there are many problems like this that are caused by the assumption that the production system is a single unique system.
  - mrunkel 6y ago
    There are many ways to solve this that don't require uniqueness across all systems. https://${customer}.hubspot.com/.. https://${customer}.hubspot.com/... https://app.hubspot.com/${customer}/.. https://app.hubspot.com/${customer}/... You'd do this at the proxy/forwarder level.
    - gomox 6y ago
      Everything has a solution, but want to bet that at least 20 different internal systems at HubSpot assume that the account ID in that URL is globally unique?
cornishpixels 6y ago
How is it not? Uniqueness would cease to matter between different tenants. They're unique by virtue of using a different database.
- gomox 6y ago
  See my sibling comment with the Hubspot example. Even though the system might work internally, other things will break if you start having duplicate account IDs because other systems don't think of the account ID as a cluster-local identifier, but as a global one.
  - ryanbrunner 6y ago
    Just thinking through this, but if it's an entirely separate environment, just host it on a separate subdomain and the account id becomes irrelevant. If you have a functioning staging environment, you already have the ability to run an isolated environment without issue, this is just a different application of the same idea.
    - gomox 6y ago
      You can probably run the environment itself, but other systems (release management, monitoring, billing, etc) probably rely on the account_id being unique.