Senior Network Security Engineer, Network Security Engineering Group - Security Engineering Section (RMI Security Eng. & Ops Dep)

Job Description: About Organization Security Engineering & Operations Department supports Rakuten Mobile and related services by providing robust security infrastructure, network security, identity/access management, and security operations platforms. As our business scales, ensuring secure and reliable operations across on-premises, cloud, and Kubernetes environments is mission-critical. To support Rakuten Mobile’s rapid growth, we are continuously expanding our Linux/Kubernetes-based platforms and enhancing our authentication and secrets management capabilities. We are seeking an experienced engineer with 8+ years of hands-on expertise to accelerate stable operations, drive standardization, and elevate the security quality of our mission-critical infrastructure. The Network Security Engineering Section designs and operates secure network services using an advanced technology stack including Linux, RHEL, Kubernetes, IPA/FreeIPA, and Vault. Job Duties Linux Infrastructure: Design, build, operate, and troubleshoot Red Hat Enterprise Linux and diverse Linux environments. Kubernetes Security: Securely operate, configure, and optimize Kubernetes clusters and related components to meet growing operational demands. Identity & Access Management: Manage authentication, user lifecycle, authorization, and policies using IPA/FreeIPA. Secrets & Certificate Management: Design and operate secrets management, PKI/certificate management, and access control using HashiCorp Vault or equivalent tools. Security Hardening: Perform security hardening, patch management, and audit support for Linux/Kubernetes environments to ensure high security standards. Automation: Drive configuration management, automation, and standardization using tools such as Ansible to improve operational efficiency. Incident Management: Handle incidents, conduct root-cause analysis (RCA), and implement preventive measures for mission-critical services. Cross-functional Collaboration: Work closely with network, cloud, security, and operations teams, utilizing English for technical communication and project coordination in a global environment. Minimum Qualifications 8+ years of hands-on experience designing, building, and operating Linux/RHEL environments. Proven experience in operating, configuring, and troubleshooting Kubernetes environments. Practical experience with authentication platforms (IPA/FreeIPA), including user and authorization management. Practical experience with secrets management, certificate management, and access control (Vault or equivalent). Strong background in Linux security hardening, patch management, and vulnerability remediation. Fundamental knowledge of networking, DNS, TLS/PKI, firewalls, and load balancers. Strong analytical skills to independently handle incidents, analyze root causes, and improve operational processes. Professional proficiency in English (technical documentation, communication, and collaboration). Preferred Qualifications Experience operating large-scale telecommunications, cloud, or mission-critical infrastructure. Automation experience using Ansible, Terraform, Python, or Shell scripting. Deep knowledge of Kubernetes security (RBAC, NetworkPolicy, container image management). Experience with monitoring, log analysis, SIEM integration, and incident response workflows. Relevant certifications such as RHCE, CKA, CKS, or other security-related credentials. Experience driving projects within global teams and managing multiple stakeholders. Work Environment Department: Network Security Engineering Section, Security Engineering Department. Collaboration: Work alongside global teams with diverse backgrounds in Linux, networking, security, cloud, and Kubernetes. Stack: RHEL, Kubernetes, IPA/FreeIPA, Vault, Ansible, Git, CI/CD, and various monitoring/logging tools across on-premises and cloud environments. Languages: English (Overall - 3 - Advanced)