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edge / apidApigeeSync / 7ac7490f073fb590d9d28ec32a8838a44db367e3
commit7ac7490f073fb590d9d28ec32a8838a44db367e3[log] [tgz]
authorScott Ganyo <scott@ganyo.com>Wed Nov 30 14:48:15 2016 -0800
committerScott Ganyo <scott@ganyo.com>Wed Nov 30 14:48:15 2016 -0800
tree4bb6d75f1067f5158e0eb83888ec4b973f697e06
parentc368e53932739e45af857c5842ecd2350f35b9dd [diff]
snapshot db protocol: emit snapshot on existing db start and document protocol in readme, cleanup
4 files changed
tree: 4bb6d75f1067f5158e0eb83888ec4b973f697e06
  1. .gitignore
  2. apigee_sync.go
  3. apigee_sync_test.go
  4. apigeeSync_suite_test.go
  5. cover.sh
  6. glide.lock
  7. glide.yaml
  8. init.go
  9. LICENSE
  10. listener.go
  11. payload.go
  12. README.md
README.md

apidApigeeSync

This core plugin for apid connects to the Apigee Change Agent and publishes the data changes events onto the apid Event service. It also coordinates DB initialization for plugins on startup.

Configuration

namedescription
apigeesync_poll_intervalint. seconds. default: 5
apigeesync_organizationstring. name. required.
apigeesync_proxy_server_basestring. url. required.
apigeesync_consumer_keystring. required.
apigeesync_consumer_secretstring. required.

Event Generated

Startup Procedure

ApigeeSync

  1. Read DB version (Snapshot.SnapshotInfo) from default DB
  2. If version found, emit Snapshot event (using Snapshot.SnapshotInfo, no data)
  3. Ask server for Snapshot
  4. Each time a Snapshot is received
    1. Verify Snapshot.SnapshotInfo is different than current
    2. Stop processing change events
    3. Remove or clean new DB version if it exists
    4. Emit Snapshot event
    5. Wait for plugins to finish processing
    6. Save Snapshot.SnapshotInfo in default DB
    7. Release old DB version
    8. Start processing change events

ToDo: ApigeeSync currently only receives a new snapshot during startup, so step #4 only happens once. However, it will eventually receive snapshots over time and the sub-steps should be followed at that time. Plugins depending on ApigeeSync for data should assume that it can happen at any time and follow the heuristic below.

ApigeeSync-dependent plugins

  1. Initialization
    1. Until receiving first Snapshot message, ApigeeSync-dependent APIs must either:
      1. not register (endpoint will return a 404 by default)
      2. return a 503 until DB is initialized
  2. Upon receiving a snapshot notification (this is a HOT DB upgrade)
    1. Get DB for version (use Snapshot.SnapshotInfo as version)
    2. Create plugin's tables, if needed
    3. Insert any snapshot data into plugin's tables
    4. Set reference to new DB for all data access
    5. If db-dependent services are not exposed yet, expose them

Example plugin code:

var (
  log      apid.LogService   // set in initPlugin
  data     apid.DataService
  unsafeDB apid.DB
  dbMux    sync.RWMutex
)

func init() {
  apid.RegisterPlugin(initPlugin)
}

func initPlugin(services apid.Services) error {
  log = services.Log().ForModule("examplePlugin")
  log.Debug("start init")
  data = services.Data()
  return nil
}

// always use getDB() to safely access current DB
func getDB() apid.DB {
  dbMux.RLock()
  db := unsafeDB
  dbMux.RUnlock()
  return db
}

func setDB(db apid.DB) {
  dbMux.Lock()
  if unsafeDB == nil { // init API on DB initialization (optional)
    go initAPI()
  }
  unsafeDB = db
  dbMux.Unlock()
}

func processSnapshot(snapshot *common.Snapshot) {

  log.Debugf("Snapshot received. Switching to DB version: %s", snapshot.SnapshotInfo)

  db, err := data.DBVersion(snapshot.SnapshotInfo)
  if err != nil {
    log.Panicf("Unable to access database: %v", err)
  }

  // init DB as needed (note: DB may exist, use 'CREATE TABLE IF NOT EXISTS' if not explicitly checking)
  initDB(db)

  for _, table := range snapshot.Tables {
    // populate tables from snapshot...
  }

  // switch to new database 
  setDB(db)
  log.Debug("Snapshot processed")
}