Kecalek_python/KEC-18_operational_cost_analysis.md

KEC-18 Operational Cost Analysis

Date: 2026-03-27

Executive Summary

• The absolute cheapest workable production setup for roughly 100 concurrent users is one Contabo Cloud VPS 10 at EUR4.50/mo, plus a domain, free Let's Encrypt TLS, free-tier SMTP, and low-cost object backup. That lands around EUR5.8-6.5/mo (USD6.7-7.5/mo) if email volume stays inside a free tier.
• The more realistic "do not hate yourself later" floor is about EUR11-16/mo (USD12.7-18.5/mo) once you include a paid SMTP plan or more backup headroom.
• For 500 to 1,000 total users, Contabo remains extremely cheap. The main constraint is not raw VPS price; it is operational headroom, backup discipline, and the app's current default connection cap.
• For 5,000 total users, I would stop using a single-node layout. Split app and MySQL onto separate VPSes and keep uploads/backups external or on a storage-optimized node.

What I Sized From The Codebase

Relevant defaults in the current code:

• protocol.py defaults to MAX_MESSAGE_BYTES=1 MiB, MAX_IMAGE_BYTES=5 MiB, MAX_FILE_BYTES=50 MiB.
• server.py defaults to MAX_CONNECTIONS_GLOBAL=200, MAX_CONNECTIONS_PER_IP=10, MAX_UPLOADS_GLOBAL=200, MAX_UPLOADS_PER_USER=5.
• db.py defaults to DB_POOL_SIZE=10.
• server.py defaults to THREAD_POOL_SIZE=40.
• README.md and scaling.md indicate the server is an asyncio TCP relay with synchronous MySQL calls pushed behind asyncio.to_thread(), which is lightweight for small deployments but still means DB latency and connection pooling matter.

Implication:

• 100 concurrent users is feasible on a very small VPS.
• More than 200 simultaneously connected devices is not feasible with the current default connection limit unless configuration is raised and load-tested.
• File storage, not CPU, becomes the first recurring cost question if usage shifts from chat-heavy to attachment-heavy.

Assumptions

To make the tiers comparable, I used these planning assumptions:

• The 500, 1,000, and 5,000 tiers are treated as total users, not fully concurrent users.
• Peak concurrent devices:
  • 100-user tier: about 100
  • 500-user tier: about 75 to 125
  • 1,000-user tier: about 125 to 175
  • 5,000-user tier: about 300 to 500
• Average retained encrypted upload footprint:
  • 100 users: 100 GB
  • 500 users: 250 GB
  • 1,000 users: 500 GB
  • 5,000 users: 1 TB
• SMTP use is limited to registration codes and lightweight transactional mail, not marketing mail.
• EUR to USD conversion uses the ECB reference 1 EUR = 1.1539 USD visible on 2026-03-27 in the ECB currency converter.

Current Vendor Pricing Used

Contabo

Official Contabo pricing page shows:

• Cloud VPS 10: 3 vCPU, 8 GB RAM, 75 GB NVMe, 32 TB traffic, EUR4.50/mo
• Cloud VPS 20: 6 vCPU, 12 GB RAM, 100 GB NVMe, 32 TB traffic, EUR7.00/mo
• Cloud VPS 30: 8 vCPU, 24 GB RAM, 200 GB NVMe, 32 TB traffic, EUR14.00/mo
• Cloud VPS 40: 12 vCPU, 48 GB RAM, 250 GB NVMe, 32 TB traffic, EUR25.00/mo
• Storage VPS 10: 2 vCPU, 4 GB RAM, 300 GB SSD, EUR4.50/mo
• Storage VPS 20: 3 vCPU, 8 GB RAM, 400 GB SSD, EUR7.00/mo

Note: Contabo also publishes separate location-fee pricing. For example, the location-fee page shows Cloud VPS 10 in United States (Central) at EUR0.95/mo extra, for EUR5.45/mo total. Base prices above are the standard pricing page numbers.

Domain, TLS, SMTP, Backup, Monitoring, Agent Costs

• Domain: Porkbun shows .com at USD11.08/yr, which is about EUR9.60/yr or EUR0.80/mo.
• TLS: Let's Encrypt certificates are free.
• SMTP:
  • MailerSend free plan: 500 emails/month
  • MailerSend Hobby: EUR5.15/mo for 5,000 emails/month
  • MailerSend Starter: pricing page shows EUR25/mo and 50,000 emails/month
• Backup/object storage:
  • Backblaze B2 pricing page shows USD6/TB/mo pay-as-you-go.
  • First 10 GB is free.
• Monitoring:
  • Self-hosted Uptime Kuma can be run on your own server at zero direct license cost.
  • Managed alternative: UptimeRobot free plan exists; paid plans start at about USD8/mo.
• OpenAI / Codex API:
  • OpenAI pricing page currently shows gpt-5.4 standard at USD2.50 / 1M input tokens and USD15.00 / 1M output tokens.
  • gpt-5.4-mini standard is USD0.75 / 1M input and USD4.50 / 1M output.

Recommended Infrastructure By Tier

Tier A: Minimum Viable, about 100 concurrent users

Recommended stack:

• 1 x Cloud VPS 10
• Let's Encrypt
• 1 .com domain
• Backblaze B2 for backups
• MailerSend free or Hobby depending email volume

Why this is enough:

• 8 GB RAM is adequate for Python app + MySQL on one box at this size.
• 75 GB NVMe is enough if uploads are modest and older media is backed up externally.
• 32 TB traffic is far above what this workload should consume.

Estimated monthly cost:

• VPS: EUR4.50 / USD5.19
• Domain amortized monthly: EUR0.80 / USD0.92
• Backup at about 100 GB retained: about EUR0.47 / USD0.54
• TLS: EUR0
• SMTP:
  • Free-tier case: EUR0
  • Safer paid case: EUR5.15 / USD5.94

Total:

• Absolute floor: about EUR5.77/mo / USD6.65/mo
• Safer operating floor: about EUR10.92/mo / USD12.60/mo

Tier B: About 500 total users

Recommended stack:

• 1 x Cloud VPS 20
• Backblaze B2 backups
• MailerSend Hobby

Why:

• More CPU and RAM headroom for MySQL buffering, background cleanup, and multi-device behavior.
• 100 GB NVMe is enough for DB + hot uploads if colder data is backed up externally.

Estimated monthly cost:

• VPS: EUR7.00 / USD8.08
• Domain: EUR0.80 / USD0.92
• Backup at about 250 GB retained: about EUR1.25 / USD1.44
• TLS: EUR0
• SMTP Hobby: EUR5.15 / USD5.94

Total:

• About EUR14.20/mo / USD16.38/mo

Tier C: About 1,000 total users

Recommended stack:

• 1 x Cloud VPS 30
• Backblaze B2 backups
• MailerSend Hobby or Starter

Why:

• 24 GB RAM gives useful cache headroom for MySQL and smoother bursts.
• This is the point where a single node is still cheap, but monitoring and restore discipline matter more than raw VPS price.

Estimated monthly cost:

• VPS: EUR14.00 / USD16.15
• Domain: EUR0.80 / USD0.92
• Backup at about 500 GB retained: about EUR2.55 / USD2.94
• TLS: EUR0
• SMTP Hobby: EUR5.15 / USD5.94

Total:

• Lean setup: about EUR22.50/mo / USD25.95/mo

If you want higher mail headroom:

• Swap SMTP to Starter at EUR25/mo
• New total: about EUR42.35/mo / USD48.87/mo

Tier D: About 5,000 total users

Recommended stack:

• 1 x Cloud VPS 20 for app server
• 1 x Cloud VPS 20 for MySQL
• Backblaze B2 backups for media + DB dumps
• MailerSend Starter

Why I would split here:

• The current codebase is still operationally simple. A two-node layout buys more reliability than buying one oversized single VPS.
• Separate failure domains help during DB spikes, backup jobs, and incident response.
• This tier likely exceeds the current default MAX_CONNECTIONS_GLOBAL=200 if user concurrency climbs, so configuration and load testing become mandatory.

Estimated monthly cost:

• App VPS: EUR7.00 / USD8.08
• DB VPS: EUR7.00 / USD8.08
• Domain: EUR0.80 / USD0.92
• Backup at about 1 TB retained: about EUR5.15 / USD5.94
• TLS: EUR0
• SMTP Starter: EUR25.00 / USD28.85

Total:

• About EUR44.95/mo / USD51.87/mo

Alternative:

• If you strongly prefer a single-node layout, Cloud VPS 40 plus backups is still cheap, but I would consider it worse operationally than two smaller nodes.

Minimum Viable Budget Answer

If the question is "what is the absolute minimum monthly spend to run this for about 100 concurrent users," the answer is:

• Roughly EUR5.8-6.5/mo (USD6.7-7.5/mo) with:
  • Cloud VPS 10
  • one cheap domain
  • free TLS
  • free SMTP tier
  • minimal external backup

If the question is "what is the minimum I would actually recommend for production without pretending backups and mail do not exist," the answer is:

• Roughly EUR11-16/mo (USD12.7-18.5/mo)

Additional Infrastructure Recommendations

TLS certificates

• Use Let's Encrypt.
• Direct recurring certificate cost: EUR0.

Domain

• Budget about EUR10/yr to EUR15/yr.
• Using current Porkbun .com pricing, a normal .com is about EUR9.60/yr.

Backups

• Do not rely only on local VPS storage.
• Cheapest clean option: nightly MySQL dumps + uploaded file backup to Backblaze B2.
• Ballpark backup cost at current B2 pricing:
  • 100 GB: about EUR0.47/mo
  • 250 GB: about EUR1.25/mo
  • 500 GB: about EUR2.55/mo
  • 1 TB: about EUR5.15/mo

SMTP relay

• Free tier is enough for early registration-code traffic.
• Move to Hobby quickly once real users arrive; it is still cheap and removes needless friction.

Monitoring

• Cheapest option: self-host Uptime Kuma.
• Managed option: UptimeRobot free or paid.
• I would treat managed monitoring as optional until there is paying traffic.

Agent Operational Cost Estimate

These costs depend entirely on token volume, not server size.

Using current OpenAI standard pricing:

• gpt-5.4: USD2.50 / 1M input, USD15.00 / 1M output
• gpt-5.4-mini: USD0.75 / 1M input, USD4.50 / 1M output

Illustrative monthly spend per active engineering agent:

• Light usage, gpt-5.4-mini:
  • 10M input + 2M output
  • about USD16.50/mo / EUR14.30/mo
• Moderate usage, gpt-5.4:
  • 10M input + 2M output
  • about USD55.00/mo / EUR47.66/mo
• Heavy usage, gpt-5.4:
  • 40M input + 8M output
  • about USD220.00/mo / EUR190.66/mo

For a small team of 3 active agents, a realistic monthly AI tooling band is:

• Lean: about EUR43-50/mo
• Moderate: about EUR143/mo
• Heavy: about EUR570+/mo

Risks And Constraints

• The code currently defaults to MAX_CONNECTIONS_GLOBAL=200. If "500 users" or "1,000 users" means concurrent devices, current defaults are not enough.
• The cheapest single-node layout mixes app, MySQL, and hot uploads on one VPS. That is acceptable early, but it increases recovery risk during disk or instance failure.
• Attachment-heavy usage can outgrow cheap NVMe faster than message traffic will outgrow CPU.
• SMTP, domain, and monitoring are trivial costs compared with the cost of not having backups.

Final Recommendation

If I had to choose one path now:

• Launch on Cloud VPS 10 if the immediate target is only about 100 concurrent users and budget is extremely tight.
• Launch on Cloud VPS 20 if you want a safer early-production baseline without materially changing cost.
• Move to a split app/DB layout by the time you are targeting 5,000 total users or any scenario above 200 concurrently connected devices.

In short: Contabo pricing is not the bottleneck here. Operational discipline, connection-limit tuning, and backup/storage policy are the real budget drivers once the app starts seeing real usage.