Elaborate about `-Cdiscovery.type=single-node`

[amotl]

About the -Cdiscovery.type=single-node, @matriv asked:

Do we explain somewhere that this is needed only for developement/testing and it shouldn't be added in prod deployments?

Originally posted by @matriv in #388 (review)

[amotl]

Hi, and thanks. We are planning to search for other spots where this is mentioned, and possibly improve the situation when applicable.

[amotl]

@mfussenegger recently stated about the vm.max_map_count=262144 requirement:

CrateDB enforces the high limit if it thinks that it is a production setup - that's based on if it is bound to a public address instead of the loopback device. Docker due to the container architecture always binds to a interface that looks public, hence it enforces the higher limit. Our examples [for single-node use] include the -Cdiscovery.type=single-node option that forces CrateDB to run in non-production mode, not enforcing any limits.

[amotl]

@matriv was able to the problem with traditional cmd (thanks!), but not with PowerShell.

We'd need to create separate or complex crate.bat script to accommodate for PowerShell. At least it has been fixed for simple crate.bat bootstrap (no docker).

The workaround for docker is to include each setting in single quotes, like '-Cdiscovery.type=single-node'.

docker run --name=cratedb --rm -it --network=cratedb-demo --publish=4200:4200 --publish=5432:5432 --env=CRATE_HEAP_SIZE=2g docker.io/crate '-Cdiscovery.type=single-node' '-Cstats.enabled=false'

So @amotl I'd like to ask you to add this note in the cratedb guide. Either recommend using cmd and not powershell, or the single quotes, or both. Many thx!

Originally posted by @matriv in #18378

[amotl]

Thank you @matriv. We will accompany the documentation with your suggestions.

Because we converted many previously manual incantations to use Docker Compose now (GH-367), we will check if adding single quotes there (command attribute) will also work well for Windows users.

We will need your help here, @michaelkremmel.

services:

  cratedb:
    image: docker.io/crate/crate:latest
    command: >
      crate -Cdiscovery.type=single-node
    ports:
      - "4200:4200/tcp"
      - "5432:5432/tcp"
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost:4200/"]
      interval: 5s
      timeout: 30s
      retries: 5

• https://cratedb.com/docs/guide/_downloads/cec3325a54a537a04ffc1c509acc0d55/compose.yaml

[amotl]

'-Cstats.enabled=false'

Is it recommended to use this particular setting for testing purposes for any reason, or did you just use that to demonstrate how two options would be stitched together, after '-Cdiscovery.type=single-node'?

[matriv]

'-Cstats.enabled=false'

Is it recommended to use this particular setting for testing purposes for any reason, or did you just use that to demonstrate how two options would be stitched together, after '-Cdiscovery.type=single-node'?

it's for demonstration.

[amotl]

NB: Honestly, for accompanying typical container operations, it would be perfect if those options could be submitted to CrateDB using environment variables, to get rid of the adjustment to the command attribute altogether, currently apparently leading to argument quoting hell. I certainly don't want to push this very ticket and conversation beyond its initial scope, but may I ask if you ever considered this approach?

Status quo

cratedb:
  image: docker.io/crate/crate:latest
  command: >
    crate -Cdiscovery.type=single-node

Idea

cratedb:
  image: docker.io/crate/crate:latest
  environment:
    CRATEDB_DISCOVERY_TYPE: single-node

[matriv]

If I get it right, I don't think that's a good idea, in docs we have all the settings as discovery.type, and with queries in sys.cluster etc. you get them like that, I don't think we should introduce another level of env parameters for docker.

[amotl]

Thanks for elaborating, I can see where the settings design is coming from, so it will be difficult to accompany with another mapping to environment variables, if I get this right? Well, we will shed some tears then move on.

[matriv]

Also, keep in mind that the problem is the docker command line run. If the params are in the DockerFile, then I guess that powershell doesn't have anything to do with this and there is no need for single quotes.

[amotl]

Thank you. Yes, it is just about command invocations where you type commands into a shell terminal. By refactoring those invocations into the Docker Compose file, the environment should be Linux only, commandline-/process-only, with no shell involved at all.

I will scan the whole GitHub org for any stray spots that still use bare CrateDB options, and send patches when applicable.