LegacyTel: Mainframe & Legacy Log Observability Agent

LegacyTel is a high-performance, lightweight, open-source log forwarding and normalization agent written in Go. It is specifically designed to bridge the observability gap between legacy platforms (IBM z/OS Mainframe, IBM AS/400 / IBM i, and HPE NonStop / Tandem) and modern security information and event management (SIEM) tools like Splunk and upstream OpenTelemetry Collectors.

LegacyTel provides a modern, zero-dependency, open-source alternative to expensive, heavy, proprietary tools, enabling unified security compliance and operations monitoring.

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Key Features

• Standard-Library Only Build: Written in pure Go standard library with zero external dependencies. This ensures a tiny memory footprint, extreme throughput, and seamless compilation/execution.
• Cross-Platform Compatibility: Easily cross-compiles to z/OS (IBM Open Enterprise SDK for Go), IBM i (running natively in the PASE environment), and HPE NonStop (x86 runtime).
• OpenTelemetry Logs Alignment: Fully parses raw events and maps them to the standardized OpenTelemetry LogRecord specification (with rich resource and attribute definitions).
• Embedded Observability Console: Serves a stunning web-based Glassmorphic Observability Console (via Server-Sent Events on :8080) providing real-time telemetry, system metrics, search/filtering, and structured JSON inspectability.
• Dual Outbound Pipelines: Built-in batch exporters for Splunk HEC (HTTP Event Collector) and standard OTLP/HTTP endpoints.

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1. Unified Security Taxonomy Mapping

LegacyTel translates native legacy operational and security logs directly to a standardized compliance taxonomy:

Taxonomy Code Directory

Category	Code	Standard Event Description	Legacy Platform mapping details
Authentication (LL)	LL01	Successful login	SMF 80 (ICH70001I) / QAUDJRN (JS/PW login success) / Tandem TACL Log On
	LL02	Successful logoff	SMF 80 (User Logoff) / QAUDJRN (JS logoff) / Tandem TACL Log Off
	LL03	User login failure	SMF 80 (ICH408I invalid password) / QAUDJRN (PW error) / Tandem TACL Failed
	LL04	Password change success	SMF 80 (ICH70002I Set Password) / QAUDJRN (PW Change success)
	LL05	Password change failure	SMF 80 (ICH408I Set Password Error) / QAUDJRN (PW Change failure)
Configuration (CC)	CC01	Application configuration change	SMF 90 (IEE252I Member updated) / QAUDJRN (SV value modified)
	CC02	Security configuration change	SMF 90 (ICH102I RACF Rules refresh) / QAUDJRN (AD Audit change)
Privileges (PA)	PA01	Successful privilege operation access	SMF 80 (ICH70002I Authorized privilege command) / Tandem SAFE Privilege Escalation
	PA02	Failed privileged operation access	SMF 80 (ICH408I Insufficient Authority) / QAUDJRN (AF Authority Fail) / Tandem SAFE Violation
Administration (SA)	SA01	User creation	SMF 80 (Define User) / QAUDJRN (CP create profile) / Tandem SAFE User Created
	SA02	User change	SMF 80 (Change User) / QAUDJRN (CP change profile) / Tandem SAFE User Changed
	SA03	User deletion	SMF 80 (Delete User) / QAUDJRN (CP delete profile) / Tandem SAFE User Deleted
	SA04	User profile/role creation	SMF 80 (Define Group/Profile) / QAUDJRN (CP role create)
	SA05	User profile/role change	SMF 80 (Change Group/Profile) / QAUDJRN (CP role change)
	SA06	User profile/role deletion	SMF 80 (Delete Group/Profile) / QAUDJRN (CP role delete)
	SA07	User password reset	SMF 80 (User Password Set) / QAUDJRN (PW Admin Reset) / Tandem SAFE Password Reset
	SA08	User account locked	QAUDJRN (Profile Disabled) / Tandem SAFE Profile Locked (Max failures)
	SA09	User account unlocked	QAUDJRN (Profile Enabled) / Tandem SAFE Profile Unlocked
System & Apps (SS)	SS01	Application started	SMF 30 Subtype 1 (Job Start) / QAUDJRN (JS job start) / Tandem TMF Coordinator Start
	SS02	Application stopped	SMF 30 Subtype 4 (Job End) / QAUDJRN (JS job end) / Tandem TMF Coordinator Stop
	SS03	Application data dump	Tandem TMF Online Dump Completed / z/OS CICS transaction dump
	SS04	Application data restore	Tandem TMF Online Restore Completed
	SS05	Application logging change	CICS/IMS logging level modification / QAUDJRN logging options update
Performance (CM)	CM01	Sequencing failure	Tandem TMF Sequencing alert / CICS transaction sequence exception
	CM02	Utilization threshold reached	SMF 30 (IEF085I CPU Limit 90%+) / AS400 Job Queue limit reached / Pathway CPU warning
	CM03	Application code change	CICS program release load / AS/400 library program compile
	CM04	Application memory change	SMF 30 (IEF196I Step Region extended) / AS/400 LPAR memory shift

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2. Ingest Architecture & Platform Integration

LegacyTel supports both local deployment (running as a native daemon directly on the host) and observability gateway mode (receiving raw data streams from mainframes and systems via TCP/UDP).

+------------------+
| z/OS Mainframe   | ---[TCP:5080 (SMF Exit / CDP)]---> +----------------------------+      +-------------------+
+------------------+                                    |    LegacyTel Agent         | ---> | Splunk Cloud /    |
+------------------+                                    |    - EBCDIC to ASCII       |      | Enterprise (HEC)  |
| IBM i (AS/400)   | ---[TCP:5081 (QAUDJRN Exit)]-----> |    - OTel Logs Standard    |      +-------------------+
+------------------+                                    |    - HTML5 Glassmorphic UI |      +-------------------+
+------------------+                                    |      Real-Time Dashboard   | ---> | Upstream OTel     |
| HPE NonStop      | ---[TCP:5082 (EMS Distributor)]--> +----------------------------+      | Collector (OTLP)  |
+------------------+                                                                        +-------------------+

IBM z/OS Ingest (SMF)

Mainframe events are parsed from native SMF records.

1. Binary Records: Captured directly from SMF datasets (e.g. SYS1.MANx) or via SMF exit programs (e.g. IEFACTRT, IRREVX01).
2. EBCDIC Conversion: LegacyTel includes a highly robust Code Page 1047 EBCDIC-to-ASCII translation block, automatically decoding binary text into readable ASCII standard format.
3. Triplets Parsing: Decodes SMF triplet structures (Offset / Length / Number fields) to traverse security sections (SMF 80) and account sections (SMF 30).

IBM i AS/400 Ingest (QAUDJRN)

Security Audit Journal records are streamed via exit programs or database integration.

1. Journal Entries: Uses standard *TYPE5 format containing sequence numbers, entry types, program names, and target objects.
2. Trigger Exit: An RPG/CL exit program triggers on new QAUDJRN entry generation and pipes the raw record over a secure TCP channel directly to the LegacyTel receiver port 5081.

HPE NonStop Ingest (EMS)

Tandem EMS (Event Management Service) structures are collected via distributors.

1. Distributor Pipe: LegacyTel binds an EMS consumer distributor ($ZEMS) streaming events to port 5082.
2. Subsystems: Decodes standard header profiles including Cpu/Pin, Event Number, and Subsystem Identifier (e.g. TACL, SAFE, TMF, PATHWAY).

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3. Securing Data in Transit (TLS & mTLS)

Security is paramount when transporting mainframe and legacy system audit logs, as they contain sensitive access metadata, user profiles, and administrative event records. LegacyTel supports native in-transit encryption and client-identity verification utilizing standard-library Transport Layer Security (TLS).

1. In-Transit Encryption (TLS)

To prevent packet sniffing and man-in-the-middle (MITM) interceptions over internal networks, TCP listeners for all receivers (zos_smf, as400_qaudjrn, tandem_ems) can be encrypted by enabling TLS:

• Forces secure modern protocol versions (TLS 1.2 or TLS 1.3).
• Implements standard standard-library key pair load (cert_file and key_file) specified in config.yaml.

2. Mutual TLS (mTLS) for Client Verification

In highly secure, zero-trust enterprise environments, it is vital to ensure that only authenticated mainframe LPARs, AS/400 logical partitions, and NonStop nodes can stream events to the observability gateway.

• Strong Authentication: Specifying a client_ca_file enables Mutual TLS (mTLS).
• Mechanism: LegacyTel acts as a secure server that challenges the legacy system sender to present a client certificate. The connection is immediately terminated if the client certificate is missing or fails verification against the specified certificate authority (CA).

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4. Operations & Configuration

LegacyTel is configured using a production-grade YAML template (config.yaml):

agent:
  id: "legacytel-hq-01"
  name: "mainframe-observability-forwarder"
  environment: "production"

server:
  host: "0.0.0.0"
  port: 8080
  enable_dashboard: true

receivers:
  zos_smf:
    enabled: true
    port: 5080
    tls_enabled: true
    cert_file: "/etc/legacytel/certs/zos_server.crt"
    key_file: "/etc/legacytel/certs/zos_server.key"
    client_ca_file: "/etc/legacytel/certs/mainframe_ca.crt" # Enables mutual TLS (mTLS)
  as400_qaudjrn:
    enabled: true
    port: 5081
    tls_enabled: true
    cert_file: "/etc/legacytel/certs/as400_server.crt"
    key_file: "/etc/legacytel/certs/as400_server.key"
    client_ca_file: "/etc/legacytel/certs/iseries_ca.crt"
  tandem_ems:
    enabled: true
    port: 5082
    tls_enabled: false

exporters:
  otlp_http:
    enabled: true
    endpoint: "http://localhost:4318/v1/logs"
  syslog:
    enabled: true
    network: "tcp" # tcp or udp
    endpoint: "siem-collector.local:514"
    format: "cef" # Pick: cef (ArcSight), leef (QRadar), or rfc5424 (Standard Syslog)
  splunk_hec:
    enabled: false # Optional direct Splunk integration

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5. Compilation & Deployment

Build the Binary Locally

Since LegacyTel is written in pure Go without external dependencies, compiling the code requires a single shell command:

# Compile local platform binary
go build -o legacytel cmd/agent/main.go

Cross-Compiling for Legacy Platforms

# 1. Cross-compile for z/OS Mainframe (EBCDIC native environment)
GOOS=zos GOARCH=s390x go build -o legacytel-zos cmd/agent/main.go

# 2. Cross-compile for IBM i (AS/400 PASE environment)
GOOS=aix GOARCH=ppc64 go build -o legacytel-iseries cmd/agent/main.go

# 3. Cross-compile for HPE NonStop Tandem x86
GOOS=nonstop GOARCH=amd64 go build -o legacytel-tandem cmd/agent/main.go

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6. Technical Tradeoffs & Performance

1. Zero-Dependency standard-library vs. Heavy Frameworks

• Tradeoff: Standard-library-only requires writing custom decoders and line-parsers (e.g. our custom YAML and EBCDIC logic).
• Advantage: Zero dependency guarantees that the binary compiles immediately on restricted mainframes (which lack packet managers like npm, pip, or go-mod proxies). The binary size is < 10MB and uses < 25MB RAM under heavy workloads.

2. High-Throughput Buffering and Dropping Policy

• Tradeoff: Mainframes generate millions of SMF records during peak hours. If upstream SIEM systems (like Splunk HEC) experience network backpressure, the agent queue could overflow.
• Resolution: LegacyTel implements an asynchronous channel buffer (5,000 slots) with non-blocking enqueuing. If the buffer is fully saturated, excess logs are safely dropped, printing a console warning, preventing the agent from exhausting target system RAM or causing mainframe resource blockages.

3. Server-Sent Events (SSE) vs. WebSockets

• Tradeoff: We opted for Server-Sent Events (SSE) instead of WebSockets for dashboard synchronization.
• Advantage: SSE operates over standard HTTP, eliminating complex WebSocket frame-parsing code, which reduces the binary footprint and provides native browser automatic reconnection with zero technical overhead.