Add example of leader failure

Signed-off-by: Byron Ruth <b@devel.io>

examples/jetstream/leader-failure/cli/Dockerfile

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+FROM natsio/nats-box:0.13.2
+
+RUN apk add bash curl
+
+COPY --from=nats:2.9.5 /nats-server /usr/local/bin/
+
+COPY . .
+
+ENTRYPOINT ["bash"]
+
+CMD ["main.sh"]
+

examples/jetstream/leader-failure/cli/main.sh

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+#!/bin/sh
+
+set -euo pipefail
+
+# Define the system account to be included by all configurations.
+cat <<- EOF > sys.conf
+accounts: {
+  SYS: {
+    users: [{user: sys, password: sys}]
+  }
+  APP: {
+    jetstream: true,
+    users: [{user: app, password: app}]
+  }
+}
+
+system_account: SYS
+EOF
+
+# Create the *east* and *west* server configurations.
+# A requirement of JetStream is to have a cluster block defined
+# since this is how available storage resources are determined
+# for placement of streams and consumers.
+#
+# In a production deployment, at least three nodes per cluster
+# are recommended which supports creating R3 streams. In this
+# test setup, only R1 streams can be created since streams replicas
+# do not cross gateway connections.
+cat <<- EOF > n1.conf
+port: 4222
+http_port: 8222
+server_name: n1
+
+include sys.conf
+
+jetstream: {
+  store_dir: "./n1"
+}
+
+cluster: {
+  name: c1,
+  port: 6222,
+  routes: [
+    "nats-route://0.0.0.0:6222",
+    "nats-route://0.0.0.0:6223",
+    "nats-route://0.0.0.0:6224",
+  ],
+}
+EOF
+
+cat <<- EOF > n2.conf
+port: 4223
+http_port: 8223
+server_name: n2
+
+include sys.conf
+
+jetstream: {
+  store_dir: "./n2"
+}
+
+cluster: {
+  name: c1,
+  port: 6223,
+  routes: [
+    "nats-route://0.0.0.0:6222",
+    "nats-route://0.0.0.0:6223",
+    "nats-route://0.0.0.0:6224",
+  ],
+}
+EOF
+
+cat <<- EOF > n3.conf
+port: 4224
+http_port: 8224
+server_name: n3
+
+include sys.conf
+
+jetstream: {
+  store_dir: "./n3"
+}
+
+cluster: {
+  name: c1,
+  port: 6224,
+  routes: [
+    "nats-route://0.0.0.0:6222",
+    "nats-route://0.0.0.0:6223",
+    "nats-route://0.0.0.0:6224",
+  ],
+}
+EOF
+
+
+# Start the servers and sleep for a few seconds to startup.
+nats-server -c n1.conf &
+N1_PID=$!
+
+nats-server -c n2.conf &
+N2_PID=$!
+
+nats-server -c n3.conf &
+N3_PID=$!
+
+sleep 3
+
+# Save and select the default context to use all seed servers.
+nats context save \
+  --server "nats://localhost:4222,nats://localhost:4223,nats://localhost:4224" \
+  --user app \
+  --password app \
+  app 
+
+nats context select app
+
+
+# Show the server list which will indicate the clusters and
+# gateway connections as well as the JetStream server report.
+nats --user sys --password sys server list
+nats --user sys --password sys server report jetstream
+
+# Add a stream.
+nats stream add \
+  --retention=limits \
+  --storage=file \
+  --replicas=3 \
+  --discard=old \
+  --dupe-window=2m \
+  --max-age=-1 \
+  --max-msgs=-1 \
+  --max-bytes=-1 \
+  --max-msg-size=-1 \
+  --max-msgs-per-subject=-1 \
+  --max-consumers=-1 \
+  --allow-rollup \
+  --no-deny-delete \
+  --no-deny-purge \
+  --subjects="orders" \
+  ORDERS
+
+# Publish some messages.
+nats req orders --count=100 'Message {{Count}}'
+
+# Force a step down of the leader.
+nats stream cluster step-down ORDERS
+
+# Report the new leader.
+nats --user sys --password sys server report jetstream
+
+# Publish more messages.
+nats req orders --count=100 'Message {{Count}}'
+
+nats stream list
+
+# Now determine the leader and kill the server.
+LEADER=$(nats stream info ORDERS --json | jq -r '.cluster.leader')
+echo "$LEADER is the leader"
+
+case $LEADER in
+  "n1")
+    kill $N1_PID
+    ;;
+  "n2")
+    kill $N2_PID
+    ;;
+  "n3")
+    kill $N3_PID
+    ;;
+esac
+
+# Publish more messages.
+nats req orders --count=100 'Message {{Count}}'
+
+nats stream list
+
+nats --user sys --password sys server report jetstream

examples/jetstream/leader-failure/docker-compose.yaml

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+version: '3.9'
+services:
+  app:
+    image: ${IMAGE_TAG}

examples/jetstream/leader-failure/meta.yaml

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+title: Leader Failure
+description: |-