CICS Short Circuit Management

Short circuit management in CICS refers to the handling of communication circuits between systems, particularly in LU6.2 (APPC) environments. It involves managing session failures, automatic reconnection, and circuit breaker patterns to ensure robust inter-system communication.

What is Short Circuit Management?

Short circuit management provides mechanisms for:

Detecting communication failures quickly
Preventing cascading failures across systems
Implementing automatic recovery procedures
Managing resource allocation during failures
Providing graceful degradation when systems are unavailable

Circuit Concepts

Session Failure Detection

CICS monitors the health of LU6.2 sessions and can detect various failure conditions:

Failure Type	Detection Method	Response
Network loss	Timeout on request	Circuit opened
Partner down	Connection reset	Automatic retry
Resource exhaustion	Threshold exceeded	Graceful degradation

Circuit Breaker Pattern

Implement a circuit breaker to prevent requests to failing systems:

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WORKING-STORAGE SECTION.
01 CIRCUIT-BREAKER.
    10 CB-STATE PIC X(1).
       88 CB-CLOSED VALUE 'C'.
       88 CB-OPEN VALUE 'O'.
       88 CB-HALF-OPEN VALUE 'H'.
    10 CB-FAILURE-COUNT PIC 9(3).
    10 CB-LAST-FAILURE-TIME PIC X(26).
    10 CB-TIMEOUT PIC S9(8) COMP VALUE 300.
 
PROCEDURE DIVISION.
    PERFORM CHECK-CIRCUIT-STATE
    
    IF CB-OPEN
        PERFORM CIRCUIT-OPEN-HANDLER
    ELSE
        PERFORM ATTEMPT-CIRCUIT-TRANSACTION
    END-IF.

Communication Circuit Management

Session State Management

Manage LU6.2 session states:

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* Establish session
EXEC CICS ALLOCATE SYSTEM(SYSTEM-ID)
    SESSION(SESSION-NAME)
    RETRY(3)
    RETRIEVAL(30)
    TIME_OUT(60)
    RESP(WS-RESPONSE)
END-EXEC.
 
* Check session status
EXEC CICS EXTRACT ATTRIBUTES SYSTEM(SESSION-NAME)
    COMMUNICATION-STATUS(WS-COMC-STATUS)
    PARTNER-NAME(WS-PARTNER)
    RESP(WS-RESPONSE)
END-EXEC.

Automatic Reconnection

Implement automatic reconnection logic:

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PROGRAM-ID. COMMUNICATION-MANAGER.
 
PROCEDURE DIVISION.
    PERFORM RESET-CIRCUIT-PARAMETERS
    PERFORM ATTEMPT-COMMUNICATION
    
    EVALUATE WS-RESPONSE
        WHEN DFHRESP(NORMAL)
            PERFORM RESET-FAILURE-COUNT
        WHEN DFHRESP(COMMFAIL)
        WHEN DFHRESP(SESSFAIL)
        WHEN DFHRESP(RCVERROR)
            PERFORM HANDLE-COMMUNICATION-FAILURE
    END-EVALUATE.
    
    EXEC CICS RETURN END-EXEC.
 
HANDLE-COMMUNICATION-FAILURE.
    ADD 1 TO WS-FAILURE-COUNT
    
    IF WS-FAILURE-COUNT > MAX-FAILURES
        MOVE 'O' TO WS-CIRCUIT-STATE  * Open circuit
        MOVE CURRENT-TIME TO WS-LAST-FAILURE-TIME
        PERFORM SET-CIRCUIT-ALARMS
    ELSE
        PERFORM WAIT-AND-RETRY
    END-IF.

Health Check Mechanisms

Implement regular health checks:

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PERFORM VARYING WS-CHECK-COUNTER FROM 1 BY 1
    UNTIL WS-CHECK-COUNTER > HEALTH-CHECK-CYCLES
    OR WS-HEALTHY-SYSTEMS = TARGET-SYSTEM-COUNT
 
    PERFORM CHECK-SYSTEM-ROUTE-' SYNC-AND-CHECK
    
    IF WS-CHECK-RESPONSE = DFHRESP(NORMAL)
        PERFORM MARK-SYSTEM-HEALTHY
        PERFORM SET-CIRCUIT-HALF-OPEN
    ELSE
        PERFORM HANDLE-CHECK-FAILURE
    END-IF
    
    PERFORM WAIT-BETWEEN-CHECKS
END-PERFORM.

Circuit Configuration

CONFIG Resource Management

Configure circuit breaker parameters:

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EXEC CICS COGNITUS CONFIG
    CB-STATE-INIT('C')
    CB-FAILURE-THRESHOLD-MAX(10)
    CB-RESET-TIME(60)
    RESP(WS-RESPONSE)
END-EXEC.

Threshold Management

Set appropriate thresholds for circuit management:

Parameter	Typical Value	Purpose
Failure threshold	5-10 failures	Open circuit trigger
Reset timeout	60-300 seconds	Automatic reset delay
Health check interval	30-60 seconds	Regular status verification
Connection timeout	30-60 seconds	Default connect wait

Circuit States Handlers

Closed Circuit Handler

Normal operation when circuit is closed:

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CLOSED-CIRCUIT-HANDLER.
    PERFORM PLACE-SYSTEM-ROUTE-AND-CHECK
    
    EVALUATE WS-RESPONSE
        WHEN DFHRESP(NORMAL)
            MOVE ZERO TO WS-CONSECUTIVE-FAILURES
            
        WHEN DFHRESP(COMMFAIL)
        WHEN DFHRESP(SESSFAIL)
            PERFORM HANDLE-SYSTEM-CONNECTIVITY-ERROR
            ADD 1 TO WS-CONSECUTIVE-FAILURES
            
            IF WS-CONSECUTIVE-FAILURES > CIRCUIT-THRESHOLD
                PERFORM OPEN-CIRCUIT-BREAKER
            END-IF
    END-EVALUATE.

Open Circuit Handler

Handle requests when circuit is open:

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OPEN-CIRCUIT-HANDLER.
    PERFORM CHECK-RESET-TIMEOUT
    
    IF RESET-TIME-EXPIRED
        SET CB-HALF-OPEN TO TRUE
        PERFORM HALF-OPEN-HANDLER
    ELSE
        PERFORM REJECT-REQUEST-OVERLOAD-FAILURE
    END-IF.
 
REJECT-REQUEST-OVERLOAD-FAILURE.
    EXEC CICS RETURN VALUE DFHMARK(DFHFUSCR)

Half-Open Circuit Handler

Test circuit recovery:

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HALF-OPEN-HANDLER.
    PERFORM PLACE-FAILURE-CAUSING-SYSTEM-ROUTE-AND-CHECK
    
    EVALUATE WS-RESPONSE
        WHEN DFHRESP(NORMAL)
            PERFORM TEST-SYSTEM-ROUTE-AND-CHECK
            IF WS-TEST-SUCCESSFUL
                PERFORM CLOSE-CIRCUIT-BREAKER
                PERFORM PROCESS-SYSTEM-ROUTE-AND-CHECK
            END-IF
            
        WHEN DFHRESP(COMMFAIL)
        WHEN DFHRESP(SESSFAIL)
            PERFORM REOPEN-CIRCUIT-BREAKER
    END-EVALUATE.
    
    * Perform multiple health checks
    PERFORM VARYING WS-CHECK FROM 1 BY 1 UNTIL WS-CHECK > 10
        PERFORM CHECK-SYSTEM-ROUTE-' SYNC-AND-CHECK
        IF WS-CHECK-RESPONSE = DFHRESP(NORMAL)
            ADD 1 TO WS-SUCCESSFUL-CHECKS
        END-IF
    END-PERFORM.
    
    IF WS-SUCCESSFUL-CHECKS > MINIMUM-SUCCESSFUL-CHECKS
        PERFORM CLOSE-CIRCUIT-BREAKER
    END-IF.

Override Procedures

Emergency Override

Provide emergency override capabilities:

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EMERGENCY-OVERRIDE.
    PERFORM PERFORM-PLACE-SYSTEMS-ROUTE-' SYNC-AFTER-TIMEOUT
    
    EVALUATE WS-RESPONSE
        WHEN DFHRESP(NORMAL)
            PERFORM LOG-OVERRIDE-SUCCESS
        WHEN DFHRESP(TIMEOUT)
            PERFORM LOG-OVERRIDE-TIMEOUT
        WHEN DFHRESP(COMMFAIL)
            PERFORM LOG-OVERRIDE-FAILURE
        WHEN DFHRESP(SESSERR)
            PERFORM LOG-SESSION-ERROR
    END-EVALUATE.

Manual Circuit Control

Allow manual circuit breaker control:

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MANUAL-CIRCUIT-CONTROL.
    ACCEPT WS-MANUAL-ACTION FROM CONSOLE.
    
    EVALUATE WS-MANUAL-ACTION
        WHEN 'OPEN'
            PERFORM OPEN-CIRCUIT-BREAKER
        WHEN 'CLOSE'
            PERFORM CLOSE-CIRCUIT-BREAKER
        WHEN 'RESET'
            PERFORM RESET-CIRCUIT-PARAMETERS
        WHEN 'STATUS'
            PERFORM DISPLAY-CIRCUIT-STATUS
        WHEN OTHER
            DISPLAY 'Invalid manual action: ' WS-MANUAL-ACTION
    END-EVALUATE.

Monitoring and Alerts

Circuit Status Monitoring

Monitor circuit breaker status:

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MONITOR-CIRCUIT-STATUS.
    PERFORM CHECK-CIRCUIT-COUNT
    
    IF WS-CIRCUIT-COUNT GREATER THAN ZERO
        DISPLAY 'Circuits currently open: ' WS-CIRCUIT-COUNT
        PERFORM LOG-CIRCUIT-STATUS
        
        IF WS-CIRCUIT-COUNT GE CIRCUIT-COUNT-HIGH-THRESHOLD
            PERFORM ALERT-CIRCUIT-MANAGER
        END-IF
    END-IF.

Performance Metrics

Track circuit breaker performance:

Number of circuit transitions per time period
Average time circuits remain open
Success rate of half-open validation checks
Response times for circuit operations

Implementation Best Practices

1. Start Simple

Begin with basic circuit breaker functionality and add complexity gradually:

Use binary circuit states initially
Implement basic failure counting
Add timeout-based reset
Gradually add advanced features

2. Monitor Circuit Performance

Continuously monitor circuit breaker effectiveness:

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PERFORM VARYING WS-CHECK-COUNTER FROM 1 BY 1
    UNTIL WS-CHECK-COUNTER > HEALTH-CHECK-CYCLES
    
    PERFORM CHECK-CIRCUIT-COUNT
    
    IF WS-CIRCUIT-COUNT GREATER THAN ZERO
        PERFORM LOG-CIRCUIT-STATUS
    END-IF
    
    PERFORM WAIT-BETWEEN-CHECKS
END-PERFORM.

3. Design for Recovery

Plan for graceful recovery from circuit failures:

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RECOVERY-PROCEDURE.
    PERFORM PLACE-SYSTEMS-ROUTE_AND_CHECKS_RECOVERY
    
    IF WS-RECOVERY-SUCCESS-FLAG = 'Y'
        PERFORM RESET-CIRCUIT-PARAMETERS
        PERFORM DISPLAY-RECOVERY-SUCCESS
    ELSE
        PERFORM TRIGGER-AUTOMATED-RESTART
    END-IF.

4. Circuit Breaker Configuration

Implement flexible configuration:

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EVALUATE WS-COGNITUS-CB-RESPONSE-STATE
    WHEN 'INITIALIZING'
        PERFORM INITIALIZE-RETRY-PARAMETERS
    WHEN 'RETRYING'
        PERFORM INCREMENT-RETRY-COUNTER
    WHEN 'FAILING'
        PERFORM OPEN-CIRCUIT-BREAKER
    WHEN 'RECOVERING'
        PERFORM HALF-OPEN-HANDLER
    WHEN 'RECOVERED'
        PERFORM CLOSE-CIRCUIT-BREAKER
END-EVALUATE.

Troubleshooting

Common Circuits Issues

Circuit Stuck Open

When circuit remains open indefinitely:

Check health check implementation
Verify reset timeout settings
Review partner system status
Consider manual circuit reset

Frequent Circuit Switching

When circuit opens and closes repeatedly:

Increase failure threshold
Extend reset timeout
Review target system load
Check for intermittent network issues

Circuit Never Opens

When circuit should open but doesn't:

Verify failure detection logic
Check threshold configuration
Review error classification
Test manual failure injection

CICS Short Circuit Management

What is Short Circuit Management?

Circuit Concepts

Session Failure Detection

Circuit Breaker Pattern

Communication Circuit Management

Session State Management

Automatic Reconnection

Health Check Mechanisms

Circuit Configuration

CONFIG Resource Management

Threshold Management

Circuit States Handlers

Closed Circuit Handler

Open Circuit Handler

Half-Open Circuit Handler

Override Procedures

Emergency Override

Manual Circuit Control

Monitoring and Alerts

Circuit Status Monitoring

Performance Metrics

Implementation Best Practices

1. Start Simple

2. Monitor Circuit Performance

3. Design for Recovery

4. Circuit Breaker Configuration

Troubleshooting

Common Circuits Issues

Circuit Stuck Open

Frequent Circuit Switching

Circuit Never Opens

LU6.2 CONFIG

CICS Connectivity

CICS Error Handling

CICS Communication