Secure Solr in production by keeping it behind a firewall, binding it only to required network interfaces, requiring authentication, restricting permissions with authorization, encrypting connections with TLS, and protecting ZooKeeper in SolrCloud deployments. These controls work together: authentication does not limit what an identified user can do, and encryption does not make an internet-facing Solr service safe.
Solr’s configuration details vary by release and deployment type. Check the documentation and upgrade notes for the exact Solr version you run before applying settings or relying on defaults.
Keep Solr off the public internet
Apache says Solr is not designed to be exposed to the open internet or other untrusted parties. Its security guide states: “No Solr API, including the Admin UI, is designed to be exposed to non-trusted parties.” A login page is not a substitute for a network boundary.
Put Solr behind a firewall and allow connections only from the application servers, administrators, and other systems that genuinely need access. Apache recommends firewall protection even when other security measures are enabled. Also limit Solr to the network interfaces it needs rather than listening broadly.
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Choose the listener deliberately
The cited production guidance describes Solr binding to 127.0.0.1 by default. That loopback setting prevents remote hosts from connecting, but a networked deployment may need a different listener. Configure the host intentionally through SOLR_JETTY_HOST, using the interface appropriate to your topology. Do not change it to a broad bind merely to make connectivity work; pair the chosen interface with firewall rules.
Restrict source addresses where appropriate
Solr’s security guide documents SOLR_IP_ALLOWLIST and SOLR_IP_DENYLIST for limiting which hosts can connect. Treat these as additional controls, not replacements for a firewall. Confirm their exact syntax and behavior in the guide for your deployed release.
Enable authentication and authorization
Authentication establishes who is making a request. Authorization decides which resources and operations that identity may use. Production access controls generally need both: Basic authentication alone identifies a user but does not restrict that user’s permissions.
Put security.json in the location your deployment expects
Solr’s authentication and authorization plugins are configured through security.json. The file must be available before startup so the plugins can initialize. Its location depends on the deployment:
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- SolrCloud: Store
security.jsonat the ZooKeeper chroot, or at the ZooKeeper root if no chroot is configured. - Standalone: Store it under
$SOLR_HOME. - User-managed cluster: Make the file available on each node.
Follow the matching version’s configuration instructions; do not assume that a file placed correctly for standalone Solr will configure a SolrCloud cluster.
Select authentication for your clients
Solr documentation lists Basic, JWT, certificate, Kerberos, and Hadoop authentication plugins. The right mechanism depends on how applications and operators establish identity and what their clients can support. Check plugin availability and configuration details for the Solr release and architecture you use.
With Basic authentication, protect the credentials in transit: the BasicAuthPlugin documentation says credentials are sent in plain text by default and recommends SSL when Basic authentication is enabled. TLS is covered below.
Grant only the permissions each role needs
Use an authorization plugin, such as rule-based authorization, when users must have different access. Rule-based permissions can restrict resources and operations, reserve security APIs for administrators, and limit collection access by role. Plan permissions around the actions each application and operator actually needs rather than giving every authenticated identity broad administrative access.
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Protect write access to security.json especially carefully. Apache warns: “A user who has access to write permissions to security.json will be able to modify all permissions and user permission assignments.” In SolrCloud, that makes access to the relevant ZooKeeper data a security-critical privilege as well.
Encrypt client and SolrCloud traffic with TLS
TLS can protect connections between clients and Solr, and it can protect node-to-node communication in SolrCloud. Configure the keystore and truststore using the SOLR_SSL_* settings documented for your Solr release. Ensure that clients trust the certificates Solr presents and that peer-name checks match the names or addresses used to connect.
Set the SolrCloud URL scheme before starting SSL-enabled nodes
For SolrCloud, set the cluster-wide urlScheme property to https in ZooKeeper before starting nodes that should communicate over SSL. Apply the procedure for the deployed release and verify that node and client URLs use HTTPS as intended.
Do not disable certificate trust or peer hostname/IP validation simply to silence certificate errors. Resolve certificate-chain, truststore, or name mismatches so that encryption also authenticates the intended peer.
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Use certificate identity carefully
Solr’s certificate authentication plugin can derive a user principal from a client certificate. The servlet container checks the certificate chain and peer hostname or IP before the request reaches the authentication plugin. If certificate fields will influence authorization, verify the contents of CA-issued certificates rather than assuming a field is trustworthy because it is present.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Secure ZooKeeper as part of SolrCloud
SolrCloud stores security.json in ZooKeeper, so ZooKeeper belongs inside the Solr security boundary. Unauthorized reads can expose security configuration, while unauthorized writes can change it. Use ZooKeeper access controls, including ACLs, to prevent unauthorized access to the data Solr relies on.
Apply the ZooKeeper ACL procedure that matches your Solr and ZooKeeper versions and deployment. The exact setup is version- and architecture-dependent; do not treat network isolation alone as a replacement for access controls on ZooKeeper data.
Run Solr with production-safe deployment practices
On supported Linux distributions, Apache’s production deployment guidance describes using the service installation script. It recommends keeping live Solr files, such as logs and index files, separate from distribution files to make upgrades easier, and says running the service as root is not recommended for production. Confirm the current instructions for your release and distribution before using the script.
- Run Solr under a dedicated, non-root service identity with only the filesystem and operating-system access it needs.
- Keep configuration, logs, index data, and distribution files organized so that service operation and upgrades do not depend on modifying the distribution in place.
- Limit administrative access to Solr and to the systems that manage its configuration.
- Recheck security defaults and configuration behavior when upgrading across major Solr versions.
For example, Solr 9’s major-change notes describe localhost as the default bind address and security-related changes to the blockUnknown default for BasicAuthPlugin and JWTAuthPlugin. These are version-specific details, not safe assumptions for every installation.
Apply the controls in deployment order
- Define reachability: Identify which clients and operators need Solr access; configure the listener and firewall for only those paths.
- Choose the deployment-specific security configuration: Put
security.jsonin the required location and configure an authentication plugin before startup. - Restrict identities: Configure authorization roles and permissions for the required APIs, operations, and collections; restrict who can change the security configuration.
- Enable TLS: Configure certificates and trust, then verify client connections. For SolrCloud, set ZooKeeper’s
urlSchemetohttpsbefore starting SSL-enabled nodes. - Protect coordination and operations: Apply ZooKeeper ACLs in SolrCloud and deploy Solr using production service practices appropriate to the operating system and release.
- Validate after changes: Confirm that permitted clients can connect, unauthorized hosts are blocked, users cannot exceed their assigned permissions, and TLS peers validate successfully.
Review the security boundary whenever the deployment changes
Adding a node, changing a listener, moving from standalone to SolrCloud, changing identity providers, or upgrading Solr can alter where configuration lives and which defaults apply. Recheck firewall reachability, plugin configuration, certificate validation, ZooKeeper permissions, and administrative access as part of those changes. Use the Apache Solr documentation and upgrade notes that match the exact deployed release rather than mixing settings from different versions.
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