README
¶
page_title: Docker Swarm strategies page_description: Swarm strategies page_keywords: docker, swarm, clustering, strategies
Strategies
The Docker Swarm scheduler features multiple strategies for ranking nodes. The strategy you choose determines how Swarm computes ranking. When you run a new container, Swarm chooses to place it on the node with the highest computed ranking for your chosen strategy.
To choose a ranking strategy, pass the --strategy flag and a strategy value to
the swarm manage command. Swarm currently supports these values:
spreadbinpackrandom
The spread and binpack strategies compute rank according to a node's
available CPU, its RAM, and the number of containers it is running. The random
strategy uses no computation. It selects a node at random and is primarily
intended for debugging.
Your goal in choosing a strategy is to best optimize your swarm according to your company's needs.
Under the spread strategy, Swarm optimizes for the node with the least number
of running containers. The binpack strategy causes Swarm to optimize for the
node which is most packed. The random strategy, like it sounds, chooses
nodes at random regardless of their available CPU or RAM.
Using the spread strategy results in containers spread thinly over many
machines. The advantage of this strategy is that if a node goes down you only
lose a few containers.
The binpack strategy avoids fragmentation because it leaves room for bigger
containers on unused machines. The strategic advantage of binpack is that you
use fewer machines as Swarm tries to pack as many containers as it can on a
node.
If you do not specify a --strategy Swarm uses spread by default.
Spread strategy example
In this example, your swarm is using the spread strategy which optimizes for
nodes that have the fewest containers. In this swarm, both node-1 and node-2
have 2G of RAM, 2 CPUs, and neither node is running a container. Under this strategy
node-1 and node-2 have the same ranking.
When you run a new container, the system chooses node-1 at random from the swarm
of two equally ranked nodes:
$ docker run -d -P -m 1G --name db mysql
f8b693db9cd6
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NODE NAMES
f8b693db9cd6 mysql:latest "mysqld" Less than a second ago running 192.168.0.42:49178->3306/tcp node-1 db
Now, we start another container and ask for 1G of RAM again.
$ docker run -d -P -m 1G --name frontend nginx
963841b138d8
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NODE NAMES
963841b138d8 nginx:latest "nginx" Less than a second ago running 192.168.0.42:49177->80/tcp node-2 frontend
f8b693db9cd6 mysql:latest "mysqld" Up About a minute running 192.168.0.42:49178->3306/tcp node-1 db
The container frontend was started on node-2 because it was the node the
least loaded already. If two nodes have the same amount of available RAM and
CPUs, the spread strategy prefers the node with least containers running.
BinPack strategy example
In this example, let's says that both node-1 and node-2 have 2G of RAM and
neither is running a container. Again, the nodes are equal. When you run a new
container, the system chooses node-1 at random from the swarm:
$ docker run -d -P -m 1G --name db mysql
f8b693db9cd6
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NODE NAMES
f8b693db9cd6 mysql:latest "mysqld" Less than a second ago running 192.168.0.42:49178->3306/tcp node-1 db
Now, you start another container, asking for 1G of RAM again.
$ docker run -d -P -m 1G --name frontend nginx
963841b138d8
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NODE NAMES
963841b138d8 nginx:latest "nginx" Less than a second ago running 192.168.0.42:49177->80/tcp node-1 frontend
f8b693db9cd6 mysql:latest "mysqld" Up About a minute running 192.168.0.42:49178->3306/tcp node-1 db
The system starts the new frontend container on node-1 because it was the
node the most packed already. This allows us to start a container requiring 2G
of RAM on node-2.
If two nodes have the same amount of available RAM and CPUs, the binpack
strategy prefers the node with most containers running.
Docker Swarm documentation index
Documentation
¶
Index ¶
Constants ¶
This section is empty.
Variables ¶
var ( // ErrNotSupported is exported ErrNotSupported = errors.New("strategy not supported") // ErrNoResourcesAvailable is exported ErrNoResourcesAvailable = errors.New("no resources available to schedule container") )
Functions ¶
Types ¶
type BinpackPlacementStrategy ¶ added in v0.2.0
type BinpackPlacementStrategy struct {
}
BinpackPlacementStrategy is exported
func (*BinpackPlacementStrategy) Initialize ¶ added in v0.2.0
func (p *BinpackPlacementStrategy) Initialize() error
Initialize is exported
func (*BinpackPlacementStrategy) Name ¶ added in v0.2.0
func (p *BinpackPlacementStrategy) Name() string
Name returns the name of the strategy
func (*BinpackPlacementStrategy) PlaceContainer ¶ added in v0.2.0
func (p *BinpackPlacementStrategy) PlaceContainer(config *cluster.ContainerConfig, nodes []*node.Node) (*node.Node, error)
PlaceContainer is exported
type PlacementStrategy ¶
type PlacementStrategy interface {
Name() string
Initialize() error
// Given a container configuration and a set of nodes, select the target
// node where the container should be scheduled.
PlaceContainer(config *cluster.ContainerConfig, nodes []*node.Node) (*node.Node, error)
}
PlacementStrategy is exported
type RandomPlacementStrategy ¶
type RandomPlacementStrategy struct {
// contains filtered or unexported fields
}
RandomPlacementStrategy randomly places the container into the cluster.
func (*RandomPlacementStrategy) Initialize ¶
func (p *RandomPlacementStrategy) Initialize() error
Initialize is exported
func (*RandomPlacementStrategy) Name ¶ added in v0.2.0
func (p *RandomPlacementStrategy) Name() string
Name returns the name of the strategy
func (*RandomPlacementStrategy) PlaceContainer ¶
func (p *RandomPlacementStrategy) PlaceContainer(config *cluster.ContainerConfig, nodes []*node.Node) (*node.Node, error)
PlaceContainer is exported
type SpreadPlacementStrategy ¶ added in v0.2.0
type SpreadPlacementStrategy struct {
}
SpreadPlacementStrategy is exported
func (*SpreadPlacementStrategy) Initialize ¶ added in v0.2.0
func (p *SpreadPlacementStrategy) Initialize() error
Initialize is exported
func (*SpreadPlacementStrategy) Name ¶ added in v0.2.0
func (p *SpreadPlacementStrategy) Name() string
Name returns the name of the strategy
func (*SpreadPlacementStrategy) PlaceContainer ¶ added in v0.2.0
func (p *SpreadPlacementStrategy) PlaceContainer(config *cluster.ContainerConfig, nodes []*node.Node) (*node.Node, error)
PlaceContainer is exported
Source Files