使用一段时间ES-5.6.3,报错License即将过期,这是怎么回事呀?

#
# License [will expire] on [Saturday, December 23, 2017]. If you have a new license, please update it.
# Otherwise, please reach out to your support contact.
#
# Commercial plugins operate with reduced functionality on license expiration:
# - security
# - Cluster health, cluster stats and indices stats operations are blocked
# - All data operations (read and write) continue to work
# - watcher
# - PUT / GET watch APIs are disabled, DELETE watch API continues to work
# - Watches execute and write to the history
# - The actions of the watches don't execute
# - monitoring
# - The agent will stop collecting cluster and indices metrics
# - The agent will stop automatically cleaning indices older than [xpack.monitoring.history.duration]
# - graph
# - Graph explore APIs are disabled
# - ml
# - Machine learning APIs are disabled
# - deprecation
# - Deprecation APIs are disabled
# - upgrade
# - Upgrade API is disabled
[2017-11-29T14:28:32,522][WARN ][o.e.l.LicenseService ] [node-002]
#
# License [will expire] on [Saturday, December 23, 2017]. If you have a new license, please update it.
# Otherwise, please reach out to your support contact.
#
# Commercial plugins operate with reduced functionality on license expiration:
# - security
# - Cluster health, cluster stats and indices stats operations are blocked
# - All data operations (read and write) continue to work
# - watcher
# - PUT / GET watch APIs are disabled, DELETE watch API continues to work
# - Watches execute and write to the history
# - The actions of the watches don't execute
# - monitoring
# - The agent will stop collecting cluster and indices metrics
# - The agent will stop automatically cleaning indices older than [xpack.monitoring.history.duration]
# - graph
# - Graph explore APIs are disabled
# - ml
# - Machine learning APIs are disabled
# - deprecation
# - Deprecation APIs are disabled
# - upgrade
# - Upgrade API is disabled