Thanks for the reply.
We are running Elasticsearch6.6.
Path to files, /usr/share/elasticsearch/config/elasticsearch.yml
and /usr/share/elasticsearch/config/unicast_hosts.txt
Here is the startup log
OpenJDK 64-Bit Server VM warning: Option UseConcMarkSweepGC was deprecated in version 9.0 and will likely be removed in a future release.
[2019-02-18T16:51:58,152][INFO ][o.e.e.NodeEnvironment ] [uTmHnAH] using [1] data paths, mounts [[/usr/share/elasticsearch/data (/dev/sda1)]], net usable_space [6.1gb], net total_space [9.6gb], types [ext4]
[2019-02-18T16:51:58,156][INFO ][o.e.e.NodeEnvironment ] [uTmHnAH] heap size [1.9gb], compressed ordinary object pointers [true]
[2019-02-18T16:51:58,159][INFO ][o.e.n.Node ] [uTmHnAH] node name derived from node ID [uTmHnAHOSiiFn8NAo9x-HA]; set [node.name] to override
[2019-02-18T16:51:58,160][INFO ][o.e.n.Node ] [uTmHnAH] version[6.6.0], pid[11], build[oss/tar/a9861f4/2019-01-24T11:27:09.439740Z], OS[Linux/4.15.0-1027-gcp/amd64], JVM[Oracle Corporation/OpenJDK 64-Bit Server VM/11.0.1/11.0.1+13]
[2019-02-18T16:51:58,161][INFO ][o.e.n.Node ] [uTmHnAH] JVM arguments [-Xms1g, -Xmx1g, -XX:+UseConcMarkSweepGC, -XX:CMSInitiatingOccupancyFraction=75, -XX:+UseCMSInitiatingOccupancyOnly, -Des.networkaddress.cache.ttl=60, -Des.networkaddress.cache.negative.ttl=10, -XX:+AlwaysPreTouch, -Xss1m, -Djava.awt.headless=true, -Dfile.encoding=UTF-8, -Djna.nosys=true, -XX:-OmitStackTraceInFastThrow, -Dio.netty.noUnsafe=true, -Dio.netty.noKeySetOptimization=true, -Dio.netty.recycler.maxCapacityPerThread=0, -Dlog4j.shutdownHookEnabled=false, -Dlog4j2.disable.jmx=true, -Djava.io.tmpdir=/tmp/elasticsearch-9153637189921725421, -XX:+HeapDumpOnOutOfMemoryError, -XX:HeapDumpPath=data, -XX:ErrorFile=logs/hs_err_pid%p.log, -Xlog:gc*,gc+age=trace,safepoint:file=logs/gc.log:utctime,pid,tags:filecount=32,filesize=64m, -Djava.locale.providers=COMPAT, -XX:UseAVX=2, -Xms2g, -Xmx2g, -Des.path.home=/usr/share/elasticsearch, -Des.path.conf=/usr/share/elasticsearch/config, -Des.distribution.flavor=oss, -Des.distribution.type=tar]
[2019-02-18T16:51:59,231][INFO ][o.e.p.PluginsService ] [uTmHnAH] loaded module [aggs-matrix-stats]
[2019-02-18T16:51:59,232][INFO ][o.e.p.PluginsService ] [uTmHnAH] loaded module [analysis-common]
[2019-02-18T16:51:59,232][INFO ][o.e.p.PluginsService ] [uTmHnAH] loaded module [ingest-common]
[2019-02-18T16:51:59,232][INFO ][o.e.p.PluginsService ] [uTmHnAH] loaded module [lang-expression]
[2019-02-18T16:51:59,232][INFO ][o.e.p.PluginsService ] [uTmHnAH] loaded module [lang-mustache]
[2019-02-18T16:51:59,233][INFO ][o.e.p.PluginsService ] [uTmHnAH] loaded module [lang-painless]
[2019-02-18T16:51:59,233][INFO ][o.e.p.PluginsService ] [uTmHnAH] loaded module [mapper-extras]
[2019-02-18T16:51:59,233][INFO ][o.e.p.PluginsService ] [uTmHnAH] loaded module [parent-join]
[2019-02-18T16:51:59,233][INFO ][o.e.p.PluginsService ] [uTmHnAH] loaded module [percolator]
[2019-02-18T16:51:59,233][INFO ][o.e.p.PluginsService ] [uTmHnAH] loaded module [rank-eval]
[2019-02-18T16:51:59,234][INFO ][o.e.p.PluginsService ] [uTmHnAH] loaded module [reindex]
[2019-02-18T16:51:59,234][INFO ][o.e.p.PluginsService ] [uTmHnAH] loaded module [repository-url]
[2019-02-18T16:51:59,234][INFO ][o.e.p.PluginsService ] [uTmHnAH] loaded module [transport-netty4]
[2019-02-18T16:51:59,234][INFO ][o.e.p.PluginsService ] [uTmHnAH] loaded module [tribe]
[2019-02-18T16:51:59,235][INFO ][o.e.p.PluginsService ] [uTmHnAH] loaded plugin [ingest-geoip]
[2019-02-18T16:51:59,235][INFO ][o.e.p.PluginsService ] [uTmHnAH] loaded plugin [ingest-user-agent]
[2019-02-18T16:52:02,348][INFO ][o.e.d.DiscoveryModule ] [uTmHnAH] using discovery type [zen] and host providers [settings, file]
[2019-02-18T16:52:02,907][INFO ][o.e.n.Node ] [uTmHnAH] initialized
[2019-02-18T16:52:02,908][INFO ][o.e.n.Node ] [uTmHnAH] starting ...
[2019-02-18T16:52:03,106][INFO ][o.e.t.TransportService ] [uTmHnAH] publish_address {10.142.0.49:9300}, bound_addresses {0.0.0.0:9300}
[2019-02-18T16:52:03,120][INFO ][o.e.b.BootstrapChecks ] [uTmHnAH] bound or publishing to a non-loopback address, enforcing bootstrap checks
[2019-02-18T16:52:06,341][INFO ][o.e.c.s.ClusterApplierService] [uTmHnAH] detected_master {kNXDw19}{kNXDw198QlWeOGDWppgzcQ}{x75T0ipzSPihJJzjBQ7Gbg}{10.142.0.48}{10.142.0.48:9300}, added {{kNXDw19}{kNXDw198QlWeOGDWppgzcQ}{x75T0ipzSPihJJzjBQ7Gbg}{10.142.0.48}{10.142.0.48:9300},}, reason: apply cluster state (from master [master {kNXDw19}{kNXDw198QlWeOGDWppgzcQ}{x75T0ipzSPihJJzjBQ7Gbg}{10.142.0.48}{10.142.0.48:9300} committed version [3]])
[2019-02-18T16:52:06,367][INFO ][o.e.h.n.Netty4HttpServerTransport] [uTmHnAH] publish_address {192.168.128.2:9200}, bound_addresses {0.0.0.0:9200}
[2019-02-18T16:52:06,367][INFO ][o.e.n.Node ] [uTmHnAH] started