Managing Elasticache

ElastiCache Management Skill

Analyze and manage ElastiCache clusters with safe, read-only operations.

MANDATORY: Two-Phase Execution

You MUST follow this two-phase pattern. Skipping Phase 1 causes hallucinated cluster/node names.

Phase 1: Discovery (ALWAYS run first)

#!/bin/bash

# 1. List Redis clusters
aws elasticache describe-cache-clusters --output json | jq '.CacheClusters[] | {CacheClusterId, Engine, EngineVersion, CacheNodeType, NumCacheNodes, CacheClusterStatus}'

# 2. List replication groups (Redis)
aws elasticache describe-replication-groups --output json | jq '.ReplicationGroups[] | {ReplicationGroupId, Status, ClusterEnabled, NodeGroups: (.NodeGroups | length)}'

# 3. List Memcached clusters (if applicable)
aws elasticache describe-cache-clusters --show-cache-node-info --output json | jq '.CacheClusters[] | select(.Engine == "memcached")'

# 4. List parameter groups
aws elasticache describe-cache-parameter-groups --output json | jq '.CacheParameterGroups[] | {CacheParameterGroupName, CacheParameterGroupFamily}'

Phase 1 outputs:

• Cache clusters with engine types and node types
• Replication groups with topology
• Parameter groups in use

Phase 2: Analysis (only after Phase 1)

Only reference cluster IDs, replication groups, and node types confirmed in Phase 1.

Shell Script Patterns

Helper Function

#!/bin/bash

# Core ElastiCache helper — always use this
ec_cmd() {
    aws elasticache "$@" --output json
}

# CloudWatch metric for ElastiCache
ec_metric() {
    local cluster_id="$1" metric="$2" stat="${3:-Average}" period="${4:-300}"
    aws cloudwatch get-metric-statistics \
        --namespace AWS/ElastiCache \
        --metric-name "$metric" \
        --dimensions Name=CacheClusterId,Value="$cluster_id" \
        --start-time "$(date -u -v-1H +%Y-%m-%dT%H:%M:%S 2>/dev/null || date -u -d '1 hour ago' +%Y-%m-%dT%H:%M:%S)" \
        --end-time "$(date -u +%Y-%m-%dT%H:%M:%S)" \
        --period "$period" \
        --statistics "$stat" \
        --output json
}

# Redis CLI helper (if direct access available)
redis_cmd() {
    local endpoint="$1" port="${2:-6379}" cmd="$3"
    redis-cli -h "$endpoint" -p "$port" --tls $cmd
}

Anti-Hallucination Rules

• NEVER reference a cluster ID without confirming via describe-cache-clusters
• NEVER reference a replication group without confirming via describe-replication-groups
• NEVER assume node types — always check cluster description
• NEVER guess parameter group names — always list first
• NEVER assume engine version — check cluster metadata

Safety Rules

• READ-ONLY ONLY: Use only describe-, list-, CloudWatch get-metric-statistics, Redis INFO/MONITOR
• FORBIDDEN: modify-cache-cluster, delete-cache-cluster, create-snapshot, reboot-cache-cluster without explicit user request
• NEVER run KEYS * on production — use SCAN instead
• Monitor memory usage before any investigation queries

Common Operations

Cluster Health Overview

#!/bin/bash
echo "=== Cache Clusters ==="
ec_cmd describe-cache-clusters --show-cache-node-info | jq '.CacheClusters[] | {CacheClusterId, Engine, EngineVersion, CacheNodeType, NumCacheNodes, CacheClusterStatus, PreferredMaintenanceWindow}'

echo ""
echo "=== Replication Groups ==="
ec_cmd describe-replication-groups | jq '.ReplicationGroups[] | {ReplicationGroupId, Status, ClusterEnabled, AutomaticFailover, MultiAZ, NodeGroups: [.NodeGroups[] | {NodeGroupId, Status, PrimaryEndpoint: .PrimaryEndpoint.Address, Slots}]}'

echo ""
echo "=== Subnet Groups ==="
ec_cmd describe-cache-subnet-groups | jq '.CacheSubnetGroups[] | {CacheSubnetGroupName, VpcId}'

Node & Replication Status

#!/bin/bash
CLUSTER_ID="${1:-my-cluster}"

echo "=== Node Details ==="
ec_cmd describe-cache-clusters --cache-cluster-id "$CLUSTER_ID" --show-cache-node-info | jq '.CacheClusters[0].CacheNodes[] | {CacheNodeId, CacheNodeStatus, Endpoint: .Endpoint.Address, ParameterGroupStatus}'

echo ""
echo "=== Replication Lag ==="
ec_metric "$CLUSTER_ID" "ReplicationLag" "Maximum" | jq -r '.Datapoints | sort_by(.Timestamp) | .[-5:][] | "\(.Timestamp)\t\(.Maximum)s"'

Performance Metrics

#!/bin/bash
CLUSTER_ID="${1:-my-cluster}"

echo "=== CPU Utilization ==="
ec_metric "$CLUSTER_ID" "CPUUtilization" "Average" | jq -r '.Datapoints | sort_by(.Timestamp) | .[-5:][] | "\(.Timestamp)\t\(.Average)%"'

echo ""
echo "=== Memory Usage ==="
ec_metric "$CLUSTER_ID" "DatabaseMemoryUsagePercentage" "Average" | jq -r '.Datapoints | sort_by(.Timestamp) | .[-5:][] | "\(.Timestamp)\t\(.Average)%"'

echo ""
echo "=== Cache Hits/Misses ==="
ec_metric "$CLUSTER_ID" "CacheHitRate" "Average" | jq -r '.Datapoints | sort_by(.Timestamp) | .[-5:][] | "\(.Timestamp)\t\(.Average)%"'

echo ""
echo "=== Evictions ==="
ec_metric "$CLUSTER_ID" "Evictions" "Sum" | jq -r '.Datapoints | sort_by(.Timestamp) | .[-5:][] | "\(.Timestamp)\t\(.Sum)"'

echo ""
echo "=== Current Connections ==="
ec_metric "$CLUSTER_ID" "CurrConnections" "Average" | jq -r '.Datapoints | sort_by(.Timestamp) | .[-5:][] | "\(.Timestamp)\t\(.Average)"'

Parameter Group Analysis

#!/bin/bash
PARAM_GROUP="${1:-default.redis7}"

echo "=== Parameter Group Settings ==="
ec_cmd describe-cache-parameters --cache-parameter-group-name "$PARAM_GROUP" | jq '.Parameters[] | select(.Source != "system") | {ParameterName, ParameterValue, DataType, IsModifiable}'

echo ""
echo "=== Key Parameters ==="
ec_cmd describe-cache-parameters --cache-parameter-group-name "$PARAM_GROUP" | jq '.Parameters[] | select(.ParameterName | test("maxmemory|timeout|tcp-keepalive|notify")) | {ParameterName, ParameterValue}'

Output Format

Present results as a structured report:

Managing Elasticache Report
═══════════════════════════
Resources discovered: [count]

Resource       Status    Key Metric    Issues
──────────────────────────────────────────────
[name]         [ok/warn] [value]       [findings]

Summary: [total] resources | [ok] healthy | [warn] warnings | [crit] critical
Action Items: [list of prioritized findings]

Target ≤50 lines of output. Use tables for multi-resource comparisons.

Counter-Rationalizations

Common Pitfalls

• Eviction pressure: High eviction rate means memory is full — check maxmemory-policy
• Replication lag: Lag spikes indicate overloaded replicas or network issues
• KEYS command: Never use KEYS on production — use SCAN with cursor
• Cluster mode: Cluster mode enabled vs disabled have different topology — verify before connecting
• Maintenance windows: Patching during maintenance windows causes brief unavailability
• Snapshot overhead: Creating snapshots on single-node clusters causes latency spikes