Install a production-style ZooKeeper ensemble on three separately reachable Ubuntu VPS servers, with Java, the same zoo.cfg on every host, a unique numeric myid in each data directory, and firewall rules that keep client, quorum, and election traffic on the networks that need it. The procedure below uses zk1, zk2, and zk3; replace those names with stable private DNS records or private IP addresses.
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What you are building
ZooKeeper is normally deployed as an ensemble rather than as an isolated server. An ensemble continues serving only when a majority of its configured servers can communicate, so the hosts should be independent machines with reliable private connectivity. Apache recommends at least three servers for fault tolerance and generally prefers an odd number because adding an even-numbered server does not improve the number of failures the majority can tolerate.
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|---|---|---|
| 3 | 2 | 1 |
| 4 | 3 | 1 |
| 5 | 3 | 2 |
A four-node deployment therefore costs another machine without improving failure tolerance over three nodes. For a first VPS deployment, place zk1, zk2, and zk3 in separate failure domains when the provider supports that option. A three-instance arrangement on one physical host is not independent enough to provide the resilience implied by an ensemble.
Choose the network and VPS layout first
Use stable private addresses
Give each VPS a private address or private DNS name that remains stable across reboots. Every server must be able to resolve and reach every other server. Do not build the ensemble around changing public addresses or hostnames that resolve differently from one node to another.
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The names used in the configuration below are:
zk1— ensemble server ID 1zk2— ensemble server ID 2zk3— ensemble server ID 3
Confirm name resolution and TCP reachability between all three hosts before installing ZooKeeper. If the VPS provider does not offer a private network, use a private overlay or VPN and restrict the resulting source addresses. Do not make quorum or election listeners generally reachable from the internet.
Evaluate a VPS on operational characteristics
For this workload, compare providers and plans using the following criteria rather than CPU count alone:
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- Private networking between all three instances
- Predictable disk latency and IOPS, especially for the transaction log
- Independent availability zones or other failure domains
- Inbound and outbound firewall controls
- Persistent-volume, snapshot, and backup support
- IPv4 and IPv6 behavior that is consistent across the private network
- Host and guest monitoring facilities
- Regional availability that matches your applications
A low-cost plan can be suitable only if it still supplies persistent storage, dependable networking, and separate instances. ZooKeeper’s correctness depends more on latency, durability, and connectivity than on peak benchmark throughput.
Prepare each Ubuntu server
Apply updates and install Java
Log in to each VPS, apply the current security updates for the selected Ubuntu release, and install a Java runtime supported by the exact ZooKeeper release you intend to deploy. Java is a prerequisite; the package name can differ between Ubuntu releases and ZooKeeper versions, so use the release documentation and your distribution’s package index rather than copying an unqualified package name.
Record the Ubuntu release, Java runtime version, and ZooKeeper version in your deployment notes. Pin the ZooKeeper version instead of silently following a moving download filename.
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Create a dedicated service account and directories
Run ZooKeeper as a non-root account. The following layout separates the program, configuration, persistent snapshots, transaction log, and ordinary logs:
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sudo mkdir -p /opt/zookeeper
sudo mkdir -p /etc/zookeeper
sudo mkdir -p /var/lib/zookeeper
sudo mkdir -p /var/lib/zookeeper-log
sudo mkdir -p /var/log/zookeeper
sudo chown -R zookeeper:zookeeper /opt/zookeeper /etc/zookeeper /var/lib/zookeeper /var/lib/zookeeper-log /var/log/zookeeperUse equivalent paths if your packaging policy requires a different prefix, but keep the paths consistent with the configuration and backup plan. The data directory must be persistent; it must not be a temporary filesystem that disappears when a VPS is recreated.
Download and verify the Apache distribution
Download the selected binary release from Apache’s official download infrastructure. Verify the published checksum or signature before unpacking it. Apache’s download index changes as releases are published, so keep the exact release filename and verification result in your change record.
Unpack the verified archive under /opt/zookeeper, make the chosen release directory readable and executable by the zookeeper account, and place the configuration file in /etc/zookeeper. Do not run the server from a directory that ordinary users can modify.
Write the ensemble configuration
Create /etc/zookeeper/zoo.cfg. This same file, including the complete server list, must be present on all three hosts:
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tickTime=2000
dataDir=/var/lib/zookeeper
dataLogDir=/var/lib/zookeeper-log
clientPort=2181
initLimit=5
syncLimit=2
server.1=zk1:2888:3888
server.2=zk2:2888:3888
server.3=zk3:2888:3888What each setting controls
tickTime=2000sets ZooKeeper’s basic time unit to 2,000 milliseconds.dataDir=/var/lib/zookeeperstores snapshots and, when no separate log directory is supplied, transaction updates.dataLogDir=/var/lib/zookeeper-logputs transaction logs on a separate path. Keep this path on fast, reliable storage.clientPort=2181is the listener used by application clients and the command-line client.initLimit=5andsyncLimit=2are the sample initialization and synchronization limits from the Apache getting-started configuration.- Each
server.id=host:quorumPort:electionPortentry identifies one ensemble member. Port 2888 carries quorum traffic; port 3888 is used for leader election.
The server list is not a list of only the local machine. Every node must contain all three entries, in a consistent form. A typo, a missing member, or a hostname that resolves differently on one host can prevent quorum formation or cause clients to discover inconsistent ensembles.
Set the required myid file
ZooKeeper maps the numeric ID in myid to the matching server.id line. Create exactly one number in /var/lib/zookeeper/myid on each server; do not add labels, spaces, or extra lines.
# on zk1
printf '1' | sudo tee /var/lib/zookeeper/myid
sudo chown zookeeper:zookeeper /var/lib/zookeeper/myid
# on zk2
printf '2' | sudo tee /var/lib/zookeeper/myid
sudo chown zookeeper:zookeeper /var/lib/zookeeper/myid
# on zk3
printf '3' | sudo tee /var/lib/zookeeper/myid
sudo chown zookeeper:zookeeper /var/lib/zookeeper/myidCheck the result before starting the process:
sudo -u zookeeper cat /var/lib/zookeeper/myidThe value printed on each host must correspond to that host’s server entry. Copying one host’s data directory or myid file to another is a common way to create duplicate IDs; create the file independently on every machine.
Restrict the three network roles with firewalls
Apache recommends deploying ZooKeeper behind a firewall. Apply controls both at the VPS provider’s network layer and on the Ubuntu host when possible.
| TCP port | Purpose | Permitted sources |
|---|---|---|
| 2181 | Client connections | Trusted application and administration networks |
| 2888 | Quorum communication | Only the private addresses of zk1, zk2, and zk3 |
| 3888 | Leader-election traffic | Only the private addresses of zk1, zk2, and zk3 |
Do not expose ports 2888 or 3888 to the public internet. Port 2181 should not be open to the world either; allow only the applications that need ZooKeeper. If an application must connect from outside the private network, carry the traffic over a private overlay or VPN, restrict source addresses tightly, and configure the authentication and TLS features supported by the selected ZooKeeper release.
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Cloud-firewall syntax varies by VPS provider. The important result is that the three servers can reach one another on 2888 and 3888, trusted clients can reach 2181, and unrelated internet hosts cannot reach any of those listeners.
Start the servers
After checking ownership, DNS, firewall rules, zoo.cfg, and myid, start the ZooKeeper process on each host with the distribution launcher:
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sudo -u zookeeper /opt/zookeeper/bin/zkServer.sh startIf your unpacked release uses a different path, invoke its bin/zkServer.sh file. Start all three members within a short maintenance window so that the ensemble can establish a majority and elect a leader. For long-running operation, run the launcher under a service supervisor appropriate to your Ubuntu policy and ensure the supervisor starts it as the zookeeper account with the intended configuration path.
Verify quorum, leadership, and client access
Check the process and listeners
On every host, confirm that the Java process is running and that the expected listeners are bound. A process being present is not proof that the ensemble is healthy: a node can run while it is isolated from the other members.
Read the server logs
Inspect the ZooKeeper logs for successful connections between members, quorum formation, and leader election. You should be able to identify one leader and the expected followers. Investigate repeated connection attempts, election restarts, authorization errors, or storage errors before directing applications to the ensemble.
Connect with the command-line client
From an allowed administration host, use the CLI shipped with the exact release you installed. A typical invocation is:
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1Scan for outdated or missing drivers - takes under a minute2Repair Windows errors before they cause bigger problems3Fix the driver behind crashes, sound loss and screen glitches/opt/zookeeper/bin/zkCli.sh -server zk1:2181Use the command syntax documented by that release. In a disposable test path, perform a harmless read and write, then remove the test node. For example, the familiar CLI sequence is:
create /installation-check "ok"
get /installation-check
delete /installation-checkDo not use an application’s production znode for this test. A successful CLI connection proves that one client path works; it does not by itself prove that all ensemble members agree.
Perform a controlled maintenance test
After the initial checks, stop one member during a planned window and verify that the remaining majority still has a leader and accepts the test client’s request. Restart the stopped member and confirm that it rejoins and catches up. Record the observed behavior for your exact release, network, and storage configuration; do not advertise failover capability until this test has actually succeeded.
Production storage and JVM practices
Protect the transaction log
Transaction-log placement is performance-critical. Keep dataLogDir on fast, reliable storage and avoid sharing the device with a workload that creates unpredictable latency. Persistent volumes should survive a process restart and be included in the backup and recovery design.
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Set the maximum Java heap only after considering the operating system, ZooKeeper’s native needs, and filesystem cache. Leaving no memory headroom can cause swapping; the administrator guidance warns that swapping severely degrades ZooKeeper performance. Load-test with your expected request rate and data shape before selecting a final heap value, and monitor garbage collection and process memory after deployment.
Back up and monitor
- Schedule snapshots or backups that match your recovery-point and recovery-time objectives.
- Document the selected release’s snapshot and restore procedure before automating recovery.
- Rotate logs so diagnostic files cannot consume the data volume.
- Alert on disk utilization, transaction-log latency, heap pressure, request latency, process restarts, and loss of quorum.
- Monitor leader and follower state using the monitoring facilities supported by the installed release.
Backups do not replace quorum. They provide a recovery path for corruption, operator error, or loss of infrastructure; normal availability still depends on a majority of live, communicating members.
Quick Recap
Troubleshoot the failures that matter most
No leader is elected
- Compare
zoo.cfgbyte-for-byte across all hosts and verify that all threeserver.*entries exist everywhere. - Check that each
myidcontains a different number matching its server entry. - Test private DNS or address resolution from every node to every other node.
- Review provider and host firewalls for TCP 2888 and 3888 in both directions.
- Check logs and disk health for repeated restarts or transaction-log errors.
A client receives connection refused or times out
- Confirm that the process is listening on the configured client port, 2181.
- Verify that the client’s source address is allowed by both firewall layers.
- Check that the client uses the private address or approved overlay route, not an unreachable public address.
- Review logs for authentication or protocol settings required by the selected release.
A member starts but does not rejoin
- Ensure its data and transaction-log paths are writable by
zookeeper. - Confirm that its clock, hostname resolution, and server ID are correct.
- Look for storage latency, a full volume, or a stale process holding the configured ports.
- Do not delete persistent data as a first response; follow the release’s documented recovery procedure and preserve backups.
The ensemble becomes slow under load
- Inspect transaction-log latency and move the log to faster storage if necessary.
- Check for swapping and reduce the heap or add memory so the operating system retains cache headroom.
- Review disk contention, network latency, and request patterns rather than adding an arbitrary fourth member.
- Use load testing to validate heap and storage choices before changing production limits.
Pre-flight checklist
- Three independent Ubuntu VPS instances have stable private addresses or DNS.
- The same pinned Apache ZooKeeper release and supported Java runtime are installed on each host.
- The service account owns the installation, configuration, data, transaction-log, and log paths.
zoo.cfgis identical on all members and lists every server.- Each data directory contains exactly one correct numeric
myid. - Clients can reach 2181 only from trusted networks.
- Only the three ensemble addresses can reach 2888 and 3888.
- Logs show a leader and connected followers after startup.
- A disposable CLI read/write test succeeds.
- A controlled one-node stop and restart has been tested.
- Persistent storage, backups, log rotation, monitoring, and alerting are documented.
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