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b56e54eaec
Now that we have a good number of longer exercises, it makes sense to rename the shorter demos/labs into 'labs' to avoid confusion between the two.
122 lines
2.8 KiB
Markdown
122 lines
2.8 KiB
Markdown
# Rolling updates
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- Let's force an update on hasher to watch it update
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.lab[
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- First lets scale up hasher to 7 replicas:
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```bash
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docker service scale dockercoins_hasher=7
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```
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- Force a rolling update (replace containers) to different image:
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```bash
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docker service update --image 127.0.0.1:5000/hasher:v0.1 dockercoins_hasher
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```
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]
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- You can run `docker events` in a separate `node1` shell to see Swarm actions
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- You can use `--force` to replace containers without a config change
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---
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## Changing the upgrade policy
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- We can change many options on how updates happen
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.lab[
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- Change the parallelism to 2, and the max failed container updates to 25%:
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```bash
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docker service update --update-parallelism 2 \
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--update-max-failure-ratio .25 dockercoins_hasher
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```
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]
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- No containers were replaced, this is called a "no op" change
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- Service metadata-only changes don't require orchestrator operations
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---
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## Changing the policy in the Compose file
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- The policy can also be updated in the Compose file
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- This is done by adding an `update_config` key under the `deploy` key:
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```yaml
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deploy:
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replicas: 10
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update_config:
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parallelism: 2
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delay: 10s
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```
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---
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## Rolling back
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- At any time (e.g. before the upgrade is complete), we can rollback:
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- by editing the Compose file and redeploying
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- by using the special `--rollback` flag with `service update`
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- by using `docker service rollback`
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.lab[
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- Try to rollback the webui service:
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```bash
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docker service rollback dockercoins_webui
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```
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]
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What happens with the web UI graph?
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---
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## The fine print with rollback
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- Rollback reverts to the previous service definition
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- see `PreviousSpec` in `docker service inspect <servicename>`
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- If we visualize successive updates as a stack:
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- it doesn't "pop" the latest update
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- it "pushes" a copy of the previous update on top
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- ergo, rolling back twice does nothing
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- "Service definition" includes rollout cadence
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- Each `docker service update` command = a new service definition
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---
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class: extra-details
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## Timeline of an upgrade
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- SwarmKit will upgrade N instances at a time
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<br/>(following the `update-parallelism` parameter)
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- New tasks are created, and their desired state is set to `Ready`
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<br/>.small[(this pulls the image if necessary, ensures resource availability, creates the container ... without starting it)]
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- If the new tasks fail to get to `Ready` state, go back to the previous step
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<br/>.small[(SwarmKit will try again and again, until the situation is addressed or desired state is updated)]
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- When the new tasks are `Ready`, it sets the old tasks desired state to `Shutdown`
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- When the old tasks are `Shutdown`, it starts the new tasks
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- Then it waits for the `update-delay`, and continues with the next batch of instances
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