What causes "Failed to build mappings for {}" in elastic/elasticsearch?

Treat as a programming/classpath defect: capture the wrapped IOException cause and report it.

elastic/elasticsearch · error · UncheckedIOException

Failed to build mappings for {}

Error message

Failed to build mappings for {}

What it means

Thrown by IngestGeoIpPlugin while serializing the hardcoded index mappings for the .geoip databases index using an XContentBuilder. The builder writes are pure in-memory string building and should never raise IOException in practice; if one occurs it is wrapped in UncheckedIOException. This is effectively an unreachable defensive guard around the mapping construction.

Source

Thrown at modules/ip-location/src/main/java/org/elasticsearch/ingest/geoip/IngestGeoIpPlugin.java:350

                .field("version", LEGACY_VERSION_FIELD_VALUE)
                .field(SystemIndexDescriptor.VERSION_META_KEY, GEOIP_INDEX_MAPPINGS_VERSION)
                .endObject()
                .field("dynamic", "strict")
                .startObject("properties")
                .startObject("name")
                .field("type", "keyword")
                .endObject()
                .startObject("chunk")
                .field("type", "integer")
                .endObject()
                .startObject("data")
                .field("type", "binary")
                .endObject()
                .endObject()
                .endObject()
                .endObject();
        } catch (IOException e) {
            throw new UncheckedIOException("Failed to build mappings for " + DATABASES_INDEX, e);
        }
    }

    @Override
    public void reload(Settings settings) {
        enterpriseGeoIpDownloaderTaskExecutor.reload(settings);
    }
}

View on GitHub (pinned to db6a809a66)

Solutions

Treat as a programming/classpath defect: capture the wrapped IOException cause and report it.
Ensure no third-party XContent override is present on the classpath.
Rule out heap exhaustion (increase heap or reduce concurrent mapping builds).

Defensive patterns

Strategy: try-catch

Try / catch

// defensive only; if this fires, inspect the wrapped IOException cause
try {
    plugin.createMappings();
} catch (UncheckedIOException e) {
    logger.error("unexpected failure building geoip index mappings", e.getCause());
    throw e;
}

Prevention

Treat occurrence as a classpath/heap defect; capture the wrapped cause.
Do not place custom XContent implementations on the classpath.
Ensure adequate heap for mapping construction.
Add a regression test that exercises the mapping builder.

When it happens

Trigger: Building DATABASES_INDEX mappings via XContentBuilder; any IOException from the builder (theoretically impossible for in-memory builders) is caught and wrapped.

Common situations: Should never occur in production. If it does, suspect a custom/buggy XContent implementation on the classpath or an OOM during allocation of the builder buffer.

Related errors

AI-assisted analysis of elastic/elasticsearch@db6a809a66 (2026-08-12). Data as JSON: /api/errors/f2079fa3d539b3cc. Report an issue: GitHub.