I have a Docker swarm Environment with 7 nodes(3 master and 4 Workers) I am trying to Deploy a Container and buy requirement is that at any point of time I need 2 instance of this container running but when I scale this the Container should be deployed to a different node than it is currently running.
Ex: say one instance of the container is running in Node 4 and I scale to scale=2 it should run in any other node except for Node 4.
tried this but no luck:
deploy:
mode: global
placement:
constraints:
- node.labels.cloud.type == nodesforservice
We solved this issue with deployment preferences configuration (under Placement section). We set up node.labels.worker, on all our worker nodes. We have 3 workers they have node.labels.worker = worker1, node.labels.worker = worker2 and node.labels.worker = worker3 labels set to each of them. On the docker compose side then we configure it:
placement:
max_replicas_per_node: 2
constraints:
- node.role==worker
preferences:
- spread: node.labels.worker
Note this will not FORCE it always on the separate node, but if it is possible it will do so. So it is not hard limit. Beware of that.
Related
If I have a Docker Swarm cluster consisting of 5 nodes, I'm aware that I can assign labels to particular nodes to guide which VMs services get deployed to. I.e. in the Docker Stack configuration:
...
deploy:
replicas: 1
placement:
constraints:
- node.labels.service == postgres
Is it possible to specify a preferred placement node? Something like this:
...
deploy:
replicas: 1
placement:
constraints:
- node.labels.service == postgres # This is always the first choice
- node.labels.service == postgres_2 # This is the second choice
i.e. the logic I'm looking for is something along the lines of:
Unless something is wrong with the node labeled postgres, deploy there. If something is wrong with that node (for example; a corrupted file system), then deploy to the node labeled postgres_2. When a node labeled postgres exists again as part of the swarm, redeploy to that node and delete the postgres service on postgres_2
i’m currently in the process of setting up a swarm with 5 machines. i’m just wondering if i can and should limit the swarm to only allow one active instance of a service? and all others just wait till they should jump in when the service fail.
This is to prevent potential concurrency problems with maria-db (as the nodes sill write to a nas), or connection limit to an external service (like node red with telegram)
If you're deploying with stack files you can set "replicas: 1" in the deploy section to make sure only one instance runs at a time.
If that instance fails (crashes or exits) docker will start another one.
https://docs.docker.com/compose/compose-file/deploy/#replicas
If the service is replicated (which is the default), replicas
specifies the number of containers that SHOULD be running at any given
time.
services: frontend:
image: awesome/webapp
deploy:
mode: replicated
replicas: 6
If you want multiple instances running and only one "active" hitting the database you'll have to coordinate that some other way.
Trying to set up a zero-downtime deployment using docker stack deploy, docker swarm one node localhost environment.
After building image demo:latest, the first deployment using the command docker stack deploy --compose-file docker-compose.yml demo able to see 4 replicas running and can access nginx default home page on port 8080 on my local machine. Now updating index.html, building image with the same name and tag running docker stack deplopy command causing below error and changes are not reflected.
Deleting the deployment and recreating will work, but I am trying to see how can updates rolled in without downtime. Please help here.
Error
Updating service demo_demo (id: wh5jcgirsdw27k0v1u5wla0x8)
image demo:latest could not be accessed on a registry to record
its digest. Each node will access demo:latest independently,
possibly leading to different nodes running different
versions of the image.
Dockerfile
FROM nginx:1.19-alpine
ADD index.html /usr/share/nginx/html/
docker-compose.yml
version: "3.7"
services:
demo:
image: demo:latest
ports:
- "8080:80"
deploy:
replicas: 4
update_config:
parallelism: 2
order: start-first
failure_action: rollback
delay: 10s
rollback_config:
parallelism: 0
order: stop-first
TLDR: push your image to a registry after you build it
Docker swarm doesn't really work without a public or private docker registry. Basically all the nodes need to get their images from the same place, and the registry is the mechanism by which that information is shared. There are other ways to get images loaded on each node in the swarm, but it involves executing the same commands on every node one at a time to load in the image, which isn't great.
Alternatively you could use docker configs for your configuration data and not rebuild the image every time. That would work passably well without a registry, and you can swap out the config data with little-no downtime:
Rotate Configs
Is there a possibility to start a service on a specific node, based on another running service? (using Docker Swarm)
To make myself a little more clear:
I want to run Nextcloud on a different node than for example, a Typo3, to spare some resources on my Nextcloud node.
How would I write that in a compose?
Look into deploy and using labels:
Example:
deploy:
mode: replicated
replicas: 1
placement:
constraints:
- node.labels.NextcloudDaemon == true
restart_policy:
condition: any
The above example will run exactly 1 container, and only on the node you've already given the label of "NextcloudDaemon".
I would like to deploy a stack to a docker swarm where I want each node to run a given service.
I looked at deploy.placement configuration and the closest option I found is the placement preference spread=node.label.abc which will equally distribute the services on nodes matching the label. However this requires updating the replicas count all the time to match the number of nodes.
Is there a way to automatically deploy a service on all the nodes without manually updating the replica count?
Is there a way to automatically deploy a service on all the nodes without manually updating the replica count?
Yes, deploy your service in global mode instead of replicated. Example from the link:
version: '3'
services:
worker:
image: dockersamples/examplevotingapp_worker
deploy:
mode: global
This will run a single instance of the container on every node matching your constraints.