Air-Gapped Registry

The defining characteristic is the complete absence of any network pathway to the internet or external networks. This is enforced through physical air gaps—no routers, no gateways, no transient connections. All data transfer occurs via sneakernet: physically moving storage media (USB drives, portable HDDs) across the gap through a controlled transfer station. This eliminates remote exfiltration vectors but introduces manual synchronization latency as a core operational constraint.

Images cannot be pulled from Docker Hub or any upstream source. Instead, a staging workstation on the connected side pulls and verifies images, then exports them as OCI-compliant tarballs using tools like skopeo copy or docker save. These archives are transferred across the gap via removable media, scanned for malware at the boundary, and loaded into the air-gapped registry using docker load or skopeo copy targeting the internal registry endpoint. This process must preserve multi-arch manifests and image digests.

Without live internet access, real-time signature verification against public transparency logs is impossible. The air-gapped registry must rely on pre-imported trust data:

• Cosign public keys and Sigstore root of trust materials must be imported alongside images.
• SBOM attestations are verified offline against known vulnerability databases that are also manually synchronized.
• Image digests become the primary integrity anchor—every pull must verify the content-addressable SHA256 hash matches the expected value before deployment.

Security scanning in an air-gapped environment requires a locally mirrored vulnerability database. Tools like Trivy and Harbor must be configured to use an internal database instance that receives periodic offline updates. The synchronization process involves:

• Exporting vulnerability feeds (NVD, OSV, proprietary) on the connected side.
• Transferring them across the gap on the same physical media schedule.
• Importing them into the internal database so scanners can evaluate images against current known vulnerabilities without external API calls.

Storage is a finite, precious resource in air-gapped environments where expanding capacity requires physical procurement. Retention policies must be strictly enforced:

• Immutable tags (digest-based) prevent accidental overwrites.
• Garbage collection reclaims space from untagged manifests and orphaned layers.
• Image promotion between internal namespaces (dev, staging, prod) uses registry-internal copy operations rather than re-importing.
• A golden image strategy ensures only hardened, approved base images consume storage.

The air-gapped registry integrates with Kubernetes admission controllers to enforce deploy-time policies without external webhook dependencies. An admission controller intercepts pod creation requests and validates:

• The image digest matches an approved signature stored in the local registry.
• The image has passed the most recent offline vulnerability scan.
• The image originates from a trusted internal project namespace. This provides a binary authorization gate that runs entirely within the isolated cluster.

A unique, content-addressable SHA256 hash that immutably identifies a specific container image manifest or layer. In air-gapped environments, digests are critical for cryptographic verification of integrity when images are transferred via physical media or one-way data diodes.

• Enables deterministic identification without relying on mutable tags
• Used to verify that manually imported blobs have not been corrupted or tampered with
• Essential for comparing local images against an upstream source of truth

A local, read-only replica of an upstream registry that acts as a pull-through cache. In a disconnected environment, the mirror is pre-seeded with required images before the network link is severed.

• Reduces bandwidth consumption during initial synchronization windows
• Provides a stable, internal endpoint for all Kubernetes nodes
• Can be configured as the default registry for container runtimes

A security mechanism using digital signatures to ensure only authorized, untampered images are executed. In air-gapped systems, trust is established through offline verification of signatures imported alongside the image.

• Uses Notary or Cosign to sign and verify manifests
• Prevents execution of images modified during physical transfer
• Enforces organizational policy even without live revocation checks

A Software Bill of Materials is a nested inventory of all components, libraries, and dependencies within a container image. In air-gapped environments, SBOMs enable offline vulnerability assessment without access to public CVE databases.

• Stored as an OCI Artifact alongside the image
• Allows security teams to audit supply chain risk locally
• Generated at build time and imported with the image

An automated process that reclaims storage by deleting unreferenced manifests and orphaned layer blobs. In resource-constrained air-gapped registries, aggressive retention policies are essential to manage limited storage capacity.

• Triggered manually or on a schedule since no external cleanup services are available
• Must be carefully configured to avoid deleting layers shared by multiple images
• Often paired with strict retention policies based on image age or tag count