Denis V.

I’m an experienced Linux System Administrator & DevOps Engineer with 20+ years in the field: 620+ projects here, 99% Job Success, Top Rated Plus. * DEVOPS FOR TEAMS OF 1 TO 50 DEVELOPERS I’ve worked both as the sole technical specialist in startups and as part of teams supporting up to 50 developers. I have a lot of experience bringing order to existing infrastructure, working around its current problems and the team’s plans. When building infrastructure from scratch, I prefer to create separate dev/staging/production environments with CI/CD integration using GitLab, GitHub Actions, or Azure DevOps. When I join an existing project to improve and optimize its processes, I usually start with an audit: infrastructure, deployment process, what’s exposed - and then provide a prioritized list of what should be fixed first, including security vulnerabilities. * SECURITY IS WHERE I SPECIALIZE A major part of my work, required by practically every project, is protecting servers, network equipment, and websites from attacks. This includes general security measures such as SSH and privilege policies, service exposure, firewalls (iptables, nftables), brute-force protection, WAF rules, and DDoS mitigation, as well as auditing and securing specific services. On top of that: log analysis and intrusion detection, file integrity monitoring, patching, retiring EOL software, and encrypted backups that an attacker can't delete. I document findings and risk using ISO/IEC 27001 audit methodology. After a breach: malware removal, IP delisting, and tracing how the attackers got in. * HIGH-LOAD SYSTEMS, CLUSTERS AND OPTIMIZATION When projects outgrow a single server due to either increasing load or high-availability requirements, I can apply my experience to build clusters that remain operational even when individual nodes fail: load balancing (HAProxy, Nginx), database replication and clustering, ProxySQL, Redis, shared storage with Ceph and GlusterFS, and Proxmox/KVM and Kubernetes clusters with failover and autoscaling. I put a lot of emphasis on optimizing existing systems. It usually involves code, the database, and server parameters at the same time, so I start with a full audit and profiling to find where the bottleneck is: CPU, disk I/O, memory, or network. Then I fix what’s limiting the system: query and index optimization, worker and connection tuning, caching, web server and storage configuration, across WordPress, Magento, Odoo, Drupal and custom stacks. I always provide before/after numbers, so you can clearly see the impact of the work. * MY PRINCIPLES FOR WORKING WITH PRODUCTION SYSTEMS - All work starts with creating a rollback point. I always have a Plan B in case something goes wrong. - I don’t leave jobs half done. If I take on a migration, it ends with the new server working and the old one safe to switch off. - Retainer clients get an emergency response within 1 hour, otherwise, same-day. - I don’t take on projects that I can’t fully complete and guarantee the result for. * EXAMPLES OF ZERO-DOWNTIME MIGRATIONS - 2,000+ cPanel accounts and 4,000+ sites moved between servers; - a bank’s 50+ server infrastructure relocated to another datacenter; - 1 TB+ database clusters; - 1,000+ mailbox systems. During migrations I plan for zero downtime, even when it isn’t easy: old and new environments run in parallel, the database replicates live, and the final delta is synchronized at cutover. Migrations are often driven by the need to reduce the cost of running services. I have experience reducing cloud infrastructure costs by 60–90% by building private cloud infrastructure or moving to more cost-effective providers such as Hetzner / OVH. One condition I always agree on with the client: lower costs must not mean lower service quality or performance. * MY APPROACH TO ACCESS AND CONFIDENTIALITY I work with production systems and client data daily. I ask for the minimum access a task needs, and credentials go through a password manager or your own secrets storage, never in plain text in chat. When the work is done, I tell you which accounts and keys should be revoked, and I remove my own access. I’m happy to sign an NDA or work under your company’s security policy. * STACK Linux: Debian, Ubuntu, RHEL, Rocky, AlmaLinux, CloudLinux Cloud: AWS, Azure, GCP Containers & IaC: Docker, Kubernetes, Terraform, Ansible, Salt Monitoring: Prometheus, Grafana, Zabbix, Wazuh Web: Nginx, Apache, HAProxy DB: MySQL, MariaDB, Percona, PostgreSQL, MongoDB, Redis Mail: Postfix, Exim, Dovecot, SPF/DKIM/DMARC Panels: cPanel/WHM, Plesk, DirectAdmin, aaPanel, CyberPanel, HestiaCP Network: BIND, PowerDNS, Route53, OpenVPN Scripting: Bash, Python, PHP If your servers are giving you trouble, deployment takes too long, or a migration is coming up, send me the details and I’ll tell you how I’d approach it.