mongodb connection refused because too many open connections: 819

Env

Debian 9

# 使用通用二进制方式安装
# mongod --version  
db version v3.4.21-2.19
git version: 2e0631f5e0d868dd51b71e1e55eb8a57300d00df
OpenSSL version: OpenSSL 1.0.2q  20 Nov 2018
allocator: tcmalloc
modules: none
build environment:
    distarch: x86_64
    target_arch: x86_64

An error

To connect given the database, the log display mongodb connection refused because too many open connections: 819.

Preliminary determination is the number of connections mongodb fulfilled.

Troubleshooting Process

1. View mongo connections

xxx:PRIMARY> db.serverStatus().connections
{ "current" : 819, "available" : 0, "totalCreated" : 1132 }

-> connections really full
2. Modify the number of connection attempts, increases mongo startup --maxConns 20000parameters, restart mongo, a number will connect ran out and said some information is maximum 20,000, the default is 1024 * 0.8
3. Check ulimit -n, this value is 1048576, in line with expectations.
4. Modify the configuration supervisord minfds=1024 100,000, after the restart to see the number of connections, in line with expectations.

xx:PRIMARY> db.serverStatus().connections
{ "current" : 1220, "available" : 78780, "totalCreated" : 2158 }

to sum up

The number of connections is limited mongod

• ulimit -n system level
• supervisord minfds parameters
• mongo maxConns parameters

Eventually, only minfds parameter set, the parameter is not set maxConns, by a supervisor controlled so that the number of connections.

reference

1. supervisor
2. maxconn
3. Depth understanding of MongoDB connection pool