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Install Memcached on a dedicated Ubuntu host, bind it to that host’s private IP, allow TCP port 11211 only from your application servers, disable UDP unless you have a documented need, and verify the service with a text-protocol set/get test. Memcached is only a transient cache: your application must use a client library, and the database or other service remains the source of truth.
What a separate Memcached server does
A separate Memcached server gives one or more application hosts a shared, in-memory cache without consuming those applications’ RAM or CPU. The cache daemon stores values under keys and evicts items when its configured memory limit is reached. It does not provide durable storage, replication, failover, or an automatic acceleration layer for arbitrary applications.
Every application that should use the cache must be explicitly configured with a Memcached client library and the cache host’s address and port. If the cache disappears, the application must be able to fetch the authoritative value from its database or service and rebuild the cache entry.
The safest basic topology is:
- A supported Ubuntu image runs Memcached on a private address.
- Application servers reach that address over the same private network or security domain.
- A host firewall or cloud security group permits TCP 11211 only from those application hosts.
- UDP is disabled unless a specific, documented client requirement exists.
- No public interface or internet-wide rule exposes Memcached.
Plan the host and network first
Choose the cache host
Use a supported Ubuntu image with enough RAM for the operating system, Memcached, and the cache working set. Record the host name or private IP that application servers will use. A private address such as 10.20.0.15 is an example only; replace it with the address actually assigned to your cache host.
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Keep the cache host and its clients on the same private network, VPC, VLAN, or equivalent security domain whenever possible. OpenStack’s Ubuntu guidance uses a controller management IP and emphasizes firewalling, authentication, and encryption controls for production deployments. A private route is not a substitute for a firewall: apply both network segmentation and an explicit source restriction.
Record the clients that need access
List the application host addresses or the smallest application subnet that should connect. You will use this list in the firewall rule. Do not use 0.0.0.0/0, an unrestricted cloud security-group rule, or a public DNS address that resolves outside your private network.
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Check the port and protocol
Memcached normally listens for its text and binary client traffic on TCP port 11211. UDP is a separate protocol and is unnecessary for most modern deployments. Plan to disable it explicitly with -U 0.
Install Memcached from Ubuntu’s package
Use the distribution package so systemd integration, configuration locations, security updates, and service ownership remain consistent with Ubuntu.
sudo apt update
sudo apt install memcached
sudo systemctl enable --now memcachedThe enable --now command both starts the daemon immediately and enables it to start at boot. Installing the package alone does not make an application use the cache; the application still needs a compatible client library and cache configuration.
Confirm that the service started before changing its network exposure:
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sudo systemctl --no-pager --full status memcachedA healthy service should show an active running state. If it is not running, inspect the service journal before changing firewall rules:
sudo journalctl -u memcached --no-pager -n 100Configure memory, binding, and protocol settings
Edit the Ubuntu configuration
Ubuntu’s package configuration is commonly stored in /etc/memcached.conf. Make a backup, then edit the file with an editor available on your host:
sudo cp /etc/memcached.conf /etc/memcached.conf.backup
sudo nano /etc/memcached.confSet explicit values appropriate to your workload. This minimal example uses a 512 MB cache, the private address 10.20.0.15, TCP port 11211, and no UDP:
-m 512
-l 10.20.0.15
-p 11211
-U 0Do not copy the example address literally. Substitute the cache host’s private address. If the application and daemon are on the same machine, bind to 127.0.0.1 instead of opening a remote interface.
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| Option | Purpose | Deployment note |
|---|---|---|
-m |
Maximum cache memory in megabytes | Choose a bounded value after measuring the working set; leave RAM for Ubuntu and other services. |
-l |
Listening address | Use the private interface address or localhost. Binding to an internal or firewalled interface is the key exposure control. |
-p |
TCP listening port | Keep 11211 unless your network design requires a different port, and match the client configuration. |
-U |
UDP port control | Use -U 0 to disable UDP when no documented requirement exists. |
-c |
Maximum simultaneous connections | Raise only when measured connection demand and available resources justify it. |
-t |
Worker thread count | Size for workload and CPU capacity rather than blindly increasing it. |
Know the package defaults before changing them
The current Ubuntu package documentation (Noble man page) lists these daemon defaults:
| Setting | Default | What the number means |
|---|---|---|
| Memory limit | 64 MB | Maximum memory assigned to cached items unless you set -m. |
| Simultaneous connections | 1,024 | Connection ceiling controlled by -c. |
| Worker threads | 4 | Default worker count controlled by -t. |
| Maximum item size | 1 MiB | One value cannot exceed this default item-size limit. |
These are package and daemon defaults, not capacity recommendations. A 64 MB cache may be too small for production, while allocating hundreds of megabytes without accounting for operating-system memory can cause pressure or swapping. Measure hit rate, item sizes, connection counts, and eviction behavior, then set explicit limits.
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Keep configuration changes reviewable
Remove or comment out conflicting -l, -p, or -U lines rather than leaving multiple competing values in the file. Preserve a copy of the working configuration so a later package update or rollback can be checked against a known baseline.
Restrict access with the firewall
Allow only application sources
For a UFW-managed host where application servers use 10.20.0.0/24, allow only that subnet to reach TCP 11211 and explicitly deny UDP:
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sudo ufw allow from 10.20.0.0/24 to any port 11211 proto tcp
sudo ufw deny 11211/udp
sudo ufw status verboseReplace the example subnet with the narrowest real source range. If only two application hosts need access, use separate host-specific rules instead of a whole subnet. A cloud security group, network ACL, or another firewall product is also valid; the requirement is the same: source-restricted TCP access and no unintended public exposure.
Verify the rule from the network perimeter
Check the cloud or virtualization firewall as well as UFW. A host rule cannot protect a service if an upstream security group permits a public path, and a correctly configured security group cannot help if UFW blocks the application subnet. Document which layer owns the rule so future changes do not silently broaden access.
Do not treat SASL as a firewall replacement
SASL can authenticate compatible clients, but it does not make an accidentally public listener safe. Keep the listener private and the source allow-list narrow even when authentication is enabled.
Restart and inspect the effective service
After saving the configuration, restart Memcached and inspect both systemd and the socket:
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sudo systemctl restart memcached
sudo systemctl --no-pager --full status memcached
sudo ss -ltnp | grep 11211The ss output should show a TCP listener on the intended private address and port. A listener on 0.0.0.0:11211 or an unexpected public address means the binding is broader than planned; stop and correct the configuration before allowing traffic.
Query the daemon’s effective settings through its text protocol. Run this from the cache host first:
printf 'stats settingsrnquitrn' | nc 10.20.0.15 11211From an application host, replace the address with the cache host’s private address. The response includes the values Memcached actually applied, including memory, connection limits, TCP and UDP ports, worker threads, binding protocol, SASL state, and item-size limits. This catches a common error: editing a file without changing the command line or service configuration that ultimately starts the daemon.
If nc is not installed on the testing host, install the distribution’s netcat package or use an existing TCP diagnostic utility. Do not install a second Memcached implementation merely to test connectivity.
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From an allowed application host, send a small value through the text protocol:
printf 'set researchcore 0 60 5rnhellornget researchcorernquitrn'
| nc 10.20.0.15 11211The command asks Memcached to store key researchcore for 60 seconds with a five-byte value. A successful response contains STORED, followed by a VALUE response containing hello. The test proves that routing, firewalling, binding, the TCP port, and the basic text protocol work from that client location.
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This is only a connectivity smoke test. It does not measure latency under load, eviction behavior, failover, maximum item size, authentication, or application-level serialization. Delete or allow the short-lived test key to expire before using the host for production traffic.
Connect application code to the cache
Configure a maintained client library
Install the maintained Memcached client for your application’s language and configure it with the private host name or IP and port 11211. Prefer a private DNS name when your environment supports it, because replacing a cache VM then requires changing DNS rather than every application configuration file.
Use connection timeouts, retry limits, and failure handling appropriate to the application. A cache outage should normally degrade to a database or service lookup, not hold every request indefinitely while clients retry a dead host.
Define the cache contract
Decide which keys are safe to cache, how values are serialized, and how long each entry should live. Include a namespace or version in keys when changing serialization formats. Treat every value as disposable: a restart, eviction, memory limit, or host replacement can remove it at any time.
Keep authoritative data elsewhere
Writes must update the authoritative database or service according to your consistency design. Memcached should hold derived or repeatable data, not the only copy of customer records, jobs, credentials, or other information that cannot be reconstructed.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Decide whether SASL is appropriate
SASL is optional and works only when the server is built with SASL support and the client supports a compatible mechanism. Confirm both capabilities before enabling it, then configure credentials and test authentication from an allowed host.
SASL authenticates clients; it is not end-to-end encryption. The official Memcached SASL documentation explicitly states that “SASL is not implemented as end-to-end encryption.” If cache contents or credentials require confidentiality, keep traffic on a private network and add an encrypted transport boundary appropriate to your architecture. Do not assume that a successful SASL handshake protects packets from network observers.
Choose the right deployment model
| Model | Network distance and latency | Failure isolation | Operations and controls | Recovery behavior |
|---|---|---|---|---|
| Local cache on each application host | Lowest network distance; no remote hop | An application host failure loses only its local cache, but entries are not shared automatically | Each host needs patching, sizing, firewalling, and monitoring | Restarting one host repopulates only that host’s cache |
| Separate Ubuntu VM | One private-network hop; latency depends on placement and congestion | Application hosts are insulated from cache memory pressure, while one VM outage can affect all clients | You control the package, binding, firewall, memory, updates, and observability | Restart or replace the VM and allow applications to repopulate entries |
| Managed cache service | Depends on the provider’s network placement and service tier | Provider may supply service-level redundancy; verify the actual contract | Less daemon patching, but access controls, client settings, limits, and costs remain your responsibility | Follow the provider’s documented restart, failover, and data-loss behavior |
All three models retain Memcached’s transient semantics. Select the model based on latency, isolation, operational ownership, observability, memory limits, and recovery requirements rather than assuming that a separate host makes the cache durable.
Troubleshoot by symptom
The service fails immediately after restart
- Run
sudo systemctl --no-pager --full status memcachedand inspectsudo journalctl -u memcached -n 100. - Check for a malformed option, duplicate conflicting setting, unavailable bind address, or a port already occupied by another process.
- Confirm that the private IP is assigned to the cache host; binding to an address that is not present prevents startup.
The daemon listens only on localhost
- Inspect
/etc/memcached.conffor an existing-l 127.0.0.1line. - Replace it with the cache host’s private address when remote applications are intended clients.
- Restart the service and confirm the address with
ss -ltnpandstats settings.
The application cannot connect
- Resolve the configured host name on the application server and confirm it returns the intended private address.
- Check that Memcached is listening on TCP 11211 and that the firewall allows the application server’s actual source IP.
- Test from the same application host, not only from the cache host; localhost success does not prove remote routing.
- Review upstream security groups, network ACLs, routes, and host firewall rules for a block or an unintended NAT path.
The test reaches the port but returns no expected value
- Use CRLF line endings exactly as shown in the text-protocol command.
- Check that the byte count in the
setcommand matches the value length;hellois five bytes. - Look for an
ERROR,CLIENT_ERROR, orSERVER_ERRORresponse and correct the command or server limit. - Remember that a 60-second expiration or eviction can remove the key; a missing key is not proof that the network failed.
Items are rejected or disappear quickly
- Compare the item size with the configured maximum, whose Ubuntu default is 1 MiB.
- Inspect the configured memory limit and eviction statistics; the 64 MB default is often too small for a real shared cache.
- Check whether application keys have unexpectedly short expiration times or whether another workload is consuming the cache.
- Measure hit rate and evictions before increasing
-m; ensure the host still has RAM for the operating system.
Connections are exhausted
- Compare active clients with the default 1,024-connection ceiling and the value returned by
stats settings. - Configure application connection pooling and close idle connections correctly before raising
-c. - Increase the limit only after checking file-descriptor limits, memory, CPU, and the application’s actual concurrency.
A security scan reports Memcached exposure
- Run
ss -ltnpand inspect the bound address, then verify UDP is disabled with-U 0and instats settings. - Remove public firewall rules and allow only named application hosts or their private subnet.
- Check cloud security groups and external load-balancer rules, not just UFW.
- If authentication is required, validate SASL support on both ends, while retaining private networking because SASL does not encrypt traffic.
Production checklist
- Supported Ubuntu image selected and private address recorded.
memcachedinstalled from Ubuntu’s package and enabled with systemd.- Explicit
-mvalue sized from measurements, with operating-system headroom. -lset to the private address, or127.0.0.1for a same-host-only design.- TCP port 11211 allowed only from application sources.
- UDP disabled with
-U 0unless a documented requirement says otherwise. - Effective settings checked with
stats settings. - Remote text-protocol set/get test completed from an actual application host.
- Application uses a maintained client library, finite timeouts, and a fallback to authoritative storage.
- Cache entries, serialization, expiration, and key namespaces documented.
- SASL enabled only when both server and client support a compatible mechanism, with separate encryption controls for confidentiality.
- Monitoring covers service health, memory use, evictions, hit rate, connections, and network reachability.
Final decision
A separate Ubuntu Memcached host is a practical shared cache when applications can reach a private network address and tolerate cache loss. The secure baseline is straightforward: install the distribution package, bind narrowly, firewall TCP 11211 by source, disable UDP, inspect the effective daemon settings, and prove remote set/get access before connecting application code. Size memory and connections from measurements, keep durable data outside Memcached, and add authentication or encrypted transport controls only when your threat model requires them.
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