336a38081a
Done with: ack '2020+' -l | xargs sed -i -e 's/2020+/2021+/g' Checked manually with: git add -p Hello to future James from 2022, and Happy Hacking!
99 lines
4.4 KiB
Go
99 lines
4.4 KiB
Go
// Mgmt
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// Copyright (C) 2013-2021+ James Shubin and the project contributors
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// Written by James Shubin <james@shubin.ca> and the project contributors
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program. If not, see <http://www.gnu.org/licenses/>.
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package chooser
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import (
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"context"
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"github.com/purpleidea/mgmt/etcd/interfaces"
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etcdtypes "go.etcd.io/etcd/pkg/types"
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)
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// Data represents the input data that is passed to the chooser.
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type Data struct {
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// Hostname is the hostname running this chooser instance. It can be
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// used as a unique key in the cluster.
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Hostname string // ourself
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Debug bool
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Logf func(format string, v ...interface{})
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}
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// Chooser represents the interface you must implement if you want to be able to
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// control which cluster members are added and removed. Remember that this can
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// get run from any peer (server) machine in the cluster, and that this may
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// change as different leaders are elected! Do not assume any state will remain
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// between invocations. If you want to maintain hysteresis or state, make sure
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// to synchronize it in etcd.
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type Chooser interface {
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// Validate validates the chooser implementation to ensure the params
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// represent a valid instantiation.
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Validate() error
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// Init initializes the chooser and passes in some useful data and
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// handles.
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Init(*Data) error
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// Connect will be called with a client interfaces.Client that you can
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// use if necessary to store some shared state between instances of this
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// and watch for external changes. Sharing state between members should
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// be avoided if possible, and there is no guarantee that your data
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// won't be deleted in a disaster. There are no backups for this,
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// regenerate anything you might need. Additionally, this may only be
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// used inside the Chooser method, since Connect is only called after
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// Init. This is however very useful for implementing special choosers.
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// Since some operations can run on connect, it gets a context. If you
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// cancel this context, then you might expect that Watch could die too.
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// Both of these should get cancelled if you call Disconnect.
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Connect(context.Context, interfaces.Client) error // we get given a namespaced client
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// Disconnect tells us to cancel our use of the client interface that we
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// got from the Connect method. We must not return until we're done.
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Disconnect() error
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// Watch is called by the engine to allow us to Watch for changes that
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// might cause us to want to re-evaluate our nomination decision. It
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// should error if it cannot startup. Once it is running, it should send
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// a nil error on every event, and an error if things go wrong. When
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// Disconnect is shutdown, then that should cause this to exit. When
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// this sends events, Choose will usually eventually get called in
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// response.
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Watch() (chan error, error)
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// Choose takes the current peer membership state, and the available
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// volunteers, and produces a list of who we should add and who should
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// quit. In general, it's best to only remove one member at a time, in
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// particular because this will get called iteratively on future events,
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// and it can remove subsequent members on the next iteration. One
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// important note: when building a new cluster, we do assume that out of
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// one available volunteer, and no members, that this first volunteer is
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// selected. Make sure that any implementations of this function do this
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// as well, since otherwise the hardcoded initial assumption would be
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// proven wrong here!
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// TODO: we could pass in two lists of hostnames instead of the full
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// URLsMap here, but let's keep it more complicated now in case, and
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// reduce it down later if needed...
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// TODO: should we add a step arg here ?
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Choose(membership, volunteers etcdtypes.URLsMap) (nominees, quitters []string, err error)
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// Close runs some cleanup routines in case there is anything that you'd
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// like to free after we're done.
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Close() error
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}
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