manager

InfraKit Manager

The Manager is a binary that offers a Group interface while providing the following:

• Leadership detection - for coordinating multiple sets (replicas) of InfraKit plugins
• State storage - persists user configuration in some backend

Both file-based and Docker Swarm (Swarm Mode) based leadership detection and state storage are available.

Group Interface

Currently the manager exposes the same Group plugin interface as the infrakit-group-default. This means infrakit group ... command will work as usual. The manager expects a group plugin to be running prior to starting up and it functions as proxy for that group plugin:

• When user does a infrakit group commit, the manager will persist the input configuration in the data store it was configured at startup time.
• If the data store is configured with a backend that is shared or replicated across multiple instances of InfraKit ensemble (all the collaborating plugins), high availability can be achieved via leader detection and global availabilit of state (the stored config).
• Multiple replicas of the manager can do leader detection so that only one is active. As soon as leadership changes, the responsibility of maintaining infrastructure state is transfered to the new manager that became active.

Leadership

The manager can use either os or swarm for leadership detection:

OS mode (via the os subcommand)

1. Assumes multiple instances of managers can access a shared file (e.g. over NFS or FUSE on S3).
2. Each manager starts up with a name (the --name flag).
3. The manager instance with the name that matches the content of the shared file is the leader.

Swarm mode (via the swarm subcommand)

1. Assumes there's a manager instance per Docker Swarm manager instance
2. Leadership depends on the status of the Swarm manager node. If the Swarm manager node is the leader, then the InfraKit manager instance running on that node is the leader.
3. When leadership changes in the Swarm, InfraKit leadership follows.

When an instance assumes leadership:

• State is retrieved from shared storage (see below) and for each group in the config, a group commit is invoked so that the new leader can begin watching the groups
• Since this is the frontend for the stateless group, it records any input the user provides when the user performs and update. The new config is then written in the shared store and update is forwarded to the actual group plugin to do the real work.

When an instance loses leadership:

• The manager uses previous configuration and 'deactivates' the local group plugin by calling free on the downstream group plugin
• It rejects user's attempt to update since it's not the leader.

State Storage

The manager can use either os or swarm for state storage:

OS mode (via the os subcommand)

1. State is stored in a local file that is well-known and defined at startup of the manager.
2. This file is a global config that can include multiple groups.

Swarm mode (via the swarm subcommand)

1. State is stored in the Swarm via annotations
2. A single global state is stored in a single annotation. The data is compressed and encoded.

Fronted (Proxy) for Group

The manager requires a group plugin to be running so that it can forward calls to it to actually perform the work of watching and updating:

• When you intend to use the manager, you should start your default group plugin with a name like group-stateless
• Then when starting the manager, set the --proxy-for-group flag to the name of the group plugin (e.g. group-stateless). By default, the manager starts up with the name of group. This matches the default name that the CLI (infrakit group ...) uses.

Running

$ make binaries
$ build/infrakit-manager -h
Manager

Usage:
  infrakit-manager [command]

Available Commands:
  os          os
  swarm       swarm mode for leader detection and storage
  version     print build version information

Flags:
      --log int                  Logging level. 0 is least verbose. Max is 5 (default 4)
      --name string              Name of the manager (default "group")
      --proxy-for-group string   Name of the group plugin to proxy for. (default "group-stateless")

Use "infrakit-manager [command] --help" for more information about a command.

Running in OS Mode

Useful for local testing:

$ infrakit-manager os --log 5

Running in Swarm Mode

First enable Swarm mode:

docker swarm init

On each Swarm manager node:

$ infrakit-manager swarm --log 5

will connect to Docker using defaulted Docker socket.

Example -- Running Locally

You can use the os subcommand of the manager to run the manager in the local, os mode where a shared file is used to determine leadership.

1. Start the plugins depending on which plugins you reference in your config. Note that the usual Group plugin is renamed group-stateless.

$ make binaries
$ build/infrakit-group-default --name group-stateless &
$ build/infrakit-instance-file
$ build/infrakit-flavor-vanilla

1. Use a local file for leadership. For example - /tmp/leader

echo group > /tmp/leader

1. Start the manager with the name group

$ build/infrakit-manager os --log 5 --proxy-for-group group-stateless --leader-file /tmp/leader --name group
DEBU[0000] Opening: /Users/myuser/.infrakit/plugins
DEBU[0000] Discovered plugin at /Users/myuser/.infrakit/plugins/group-stateless
DEBU[0000] Discovered plugin at /Users/myuser/.infrakit/plugins/infrakit-flavor-vanilla
DEBU[0000] Discovered plugin at /Users/myuser/.infrakit/plugins/infrakit-instance-file
INFO[0000] Starting up manager: &{group 0xc4202ce7e0 0xc4202e8810 0xc4202ce940 group-stateless}
DEBU[0000] Opening: /Users/myuser/.infrakit/plugins
DEBU[0000] Discovered plugin at /Users/myuser/.infrakit/plugins/group-stateless
DEBU[0000] Discovered plugin at /Users/myuser/.infrakit/plugins/infrakit-flavor-vanilla
DEBU[0000] Discovered plugin at /Users/myuser/.infrakit/plugins/infrakit-instance-file
INFO[0000] Manager starting
INFO[0000] Listening at: /Users/myuser/.infrakit/plugins/group
DEBU[0005] ID (group) - checked /tmp/leader for leadership: group, err=<nil>, leader=true
DEBU[0005] leader: true
INFO[0005] Assuming leadership
INFO[0005] Loaded snapshot. err= <nil>
INFO[0005] Start watching groups
DEBU[0005] Opening: /Users/myuser/.infrakit/plugins
DEBU[0005] Discovered plugin at /Users/myuser/.infrakit/plugins/group
DEBU[0005] Discovered plugin at /Users/myuser/.infrakit/plugins/group-stateless
DEBU[0005] Discovered plugin at /Users/myuser/.infrakit/plugins/infrakit-flavor-vanilla
DEBU[0005] Discovered plugin at /Users/myuser/.infrakit/plugins/infrakit-instance-file
INFO[0005] Processing group managers with plugin group-stateless
DEBU[0005] exec on group managers plugin= group-stateless
INFO[0005] WATCH group managers with spec: {managers 0xc420122600}
INFO[0005] Processing group workers with plugin group-stateless
DEBU[0005] exec on group workers plugin= group-stateless
INFO[0005] WATCH group workers with spec: {workers 0xc420122a60}
DEBU[0010] ID (group) - checked /tmp/leader for leadership: group, err=<nil>, leader=true
DEBU[0015] ID (group) - checked /tmp/leader for leadership: group, err=<nil>, leader=true
DEBU[0020] ID (group) - checked /tmp/leader for leadership: group, err=<nil>, leader=true
DEBU[0025] ID (group) - checked /tmp/leader for leadership: group, err=<nil>, leader=true
DEBU[0030] ID (group) - checked /tmp/leader for leadership: group, err=<nil>, leader=true

You should see that the current instance is detecting that it's the leader, since $(cat /tmp/leader) == 'group'. You can change the leadership by changing the content of the file /tmp/leader:

$ echo group2 > /tmp/leader

You should see the instance detecting its non-leader status and will unwatch groups if any.

DEBU[0150] leader: false
INFO[0150] Lost leadership
INFO[0150] Unwatching groups
DEBU[0150] Opening: /Users/myuser/.infrakit/plugins
DEBU[0150] Discovered plugin at /Users/myuser/.infrakit/plugins/group
DEBU[0150] Discovered plugin at /Users/myuser/.infrakit/plugins/group-stateless
DEBU[0150] Discovered plugin at /Users/myuser/.infrakit/plugins/infrakit-flavor-vanilla
DEBU[0150] Discovered plugin at /Users/myuser/.infrakit/plugins/infrakit-instance-file
INFO[0150] Processing group managers with plugin group-stateless
DEBU[0150] exec on group managers plugin= group-stateless
INFO[0150] UNWATCH group managers with spec: {managers 0xc420123580}
INFO[0150] Processing group workers with plugin group-stateless
DEBU[0150] exec on group workers plugin= group-stateless
INFO[0150] UNWATCH group workers with spec: {workers 0xc4200cb880}
DEBU[0155] ID (group) - checked /tmp/leader for leadership: group2, err=<nil>, leader=false
DEBU[0160] ID (group) - checked /tmp/leader for leadership: group2, err=<nil>, leader=false