Start the instances

After the build, the engine starts the wanted number of instances from the snapshot.

Each new instance joins the private network. Its DNS alias is the name of the service.

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The deploy first takes the service lock and saves the snapshot. Then it starts the instances. The state of the deploy is deploying.

Deploy log

==> Limits: 512 MiB memory, 1 CPU per instance

What each container gets

Setting	Value
Network	The private network, with the service name as DNS alias
Restart policy	`unless-stopped`
Published port	`127.0.0.1:<random port>`. See Why 127.0.0.1.
Memory	The memory limit, with no swap above it
CPU	The CPU limit
Processes	`--pids-limit`
Logs	Log rotation (`--log-max-size`, `--log-max-files`), when the default log driver of the Docker daemon is `json-file`

The snapshot

Before it starts instances, a deploy fixes all that they run with and saves it as a snapshot.

Blue-green and recreate

The engine starts new instances next to the old ones, or after them for a service with a disk.