Refactor FailoverController/HAAdmin code to add an abstract class for "target"
services
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Key: HADOOP-8193
URL: https://issues.apache.org/jira/browse/HADOOP-8193
Project: Hadoop Common
Issue Type: Improvement
Components: ha
Affects Versions: 0.24.0, 0.23.3
Reporter: Todd Lipcon
Assignee: Todd Lipcon
In working at HADOOP-8077, HDFS-3084, and HDFS-3072, I ran into various
difficulties which are an artifact of the current design. A few of these:
- the service name is "resolved" from the logical name (eg ns1.nn1) to an IP
address at the outer layer of DFSHAAdmin
-- this means it's difficult to provide the logical name "ns1.nn1" to fence
scripts (HDFS-3084)
-- this means it's difficult to configure fencing method per-namespace (since
the FailoverController doesn't know what the namespace is) (HADOOP-8077)
- the configuration for HA HDFS is weirdly split between core-site and
hdfs-site, even though most users see this as an HDFS feature. For example,
users expect to configure NN fencing configurations in hdfs-site, and expect
the keys to have a dfs.* prefix
- proxies are constructed at the outer layer of the admin commands. This means
it's impossible for the inner layers (eg FailoverController.failover) to
re-construct proxies with different timeouts (HDFS-3072)
The proposed refactor is to add a new interface (tentatively named
HAServiceTarget) which refers to target for one of the admin commands. An
instance of this class is responsible for creating proxies, creating fencers,
mapping back to a logical name, etc. The HDFS implementation of this class can
then provide different results based on the particular nameservice, can use
HDFS-specific configuration prefixes, etc. Using this class as the argument for
fencing methods also makes the API more evolvable in the future, since we can
add new getters to HAServiceTarget (whereas the current InetSocketAddress is
quite limiting)
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