merging 3 files in awk based on common keys

With GNU awk, could you please try following written and tested with shown samples.

awk '
ARGIND==1{
  if($0~/server-[0-9]+/){
    foundServer=1
    serverName=$2
  }
  if(foundServer && $0 ~ /ip_addr:/){
    servername[serverName]=$2
    serverName=foundServer=""
  }
  next
}
ARGIND==2{
  if(setFS==""){ FS=OFS=",";setFS=1 }
  server[$2]=$1
  powerarr[$2]=$3 OFS $4 OFS $5
  next
}
ARGIND==3{
  if($1 in server){
    print $2 OFS server[$1] OFS $3 OFS $4 OFS $5 OFS $6 OFS powerarr[$1],(servername[server[$1]]!=""?servername[server[$1]]:"NA")
  }
}
' hosts.yaml bm.txt n.txt

Explanation: Adding a detailed explanation for above.

awk '
##Starting awk program from here.
ARGIND==1{
##Checking condition if this is first Input_file then do following.
  if($0~/server-[0-9]+/){
##Checking condition if line has server with digits then do following.
    foundServer=1
##Setting foundServer to 1 here.
    serverName=$2
##Setting serverName to 2nd field which is value from  yaml file.
  }
  if(foundServer && $0 ~ /ip_addr:/){
##Checking condition if foundServer is SET and line has ip_addr in it then do following.
    servername[serverName]=$2
##Creating servername array with index of serverName with value of 2nd field.
    serverName=foundServer=""
##Nullifying serverName and foundServer here.
  }
  next
##next will skip all further statements from here.
}
ARGIND==2{
##Checking condition if this is 2nd Input_file is being read then do following.
  if(setFS==""){ FS=OFS=",";setFS=1 }
##Checking condition if setFS is NULL then set FS and OFS as comma here and setting setFS to 1.
  server[$2]=$1
##Creating server with index of 2nd field which has 1st field as value.
  powerarr[$2]=$3 OFS $4 OFS $5
##Creating powerarr with index as 2nd field and $3 OFS $4 OFS $5 as value.
  next
##next will skip all further statements from here.
}
ARGIND==3{
##Checking condition if this is 3rd Input_file is being read then do following.
  if($1 in server){
##Checking condition if 1st field is present in server then do following.
    print $2 OFS server[$1] OFS $3 OFS $4 OFS $5 OFS $6 OFS powerarr[$1],(servername[server[$1]]!=""?servername[server[$1]]:"NA")
##Printing needed values as per OP here.
  }
}
' hosts.yaml bm.txt n.txt ##Mentioning Input_file names here.

awk 'FILENAME=="n.txt" { # Process on the n.txt file
                split($0,arr,","); # Split data into array arr using , as the delimiter
                nam[arr[1]]=arr[2]; # Use entries in arr array to create separate arrays for each piece of data required.
                state[arr[1]]=arr[5];
                cp[arr[1]]=arr[6];
                state3[arr[1]]=arr[3];
                ndesc[arr[1]]=arr[4];
                next
               }
FILENAME=="bm.txt" { # Process only bm.txt.
                split($0,arr,",");
                serv[arr[2]]=arr[1]; # Create separate arrays as we did with the previous file
                power[arr[2]]=arr[3];
                state1[arr[2]]=arr[4];
                berr[arr[2]]=arr[5];
                next
               }
FILENAME=="hosts.yaml" && /name/ { # Search for name variable in yaml
                split($0,arr,":");
                gsub(" ","",arr[2]); # Remove spaces
                serva=arr[2]; # Hold server name in serva variable
                next
               }
FILENAME=="hosts.yaml" && /ip_addr/ { # Search for ip_addr in yaml
                split($0,arr,":");
                gsub(" ","",arr[2]);
                serv1[serva]=arr[2]; # Set up an array indexed with server name
                next
               }
END                {
                for (i in nam) { # Loop through nam array pulling out entries in other arrays
                   print nam[i]","serv[i]","state3[i]","ndesc[i]","state[i]","cp[i]","power[i]","state1[i]","berr[i]","serv1[serv[i]]
                }
               } n.txt bm.txt host.yaml

Output:

oc-ctrl-jr-1,server-11,ACTIVE,-,Running,cp=172.31.0.6,power on,active,False,
oc-ctrl-jr-2,server-2,ACTIVE,-,Running,cp=172.31.0.5,power on,active,False,
oc-comp-jr-0,server-25,ACTIVE,-,Running,cp=172.31.0.9,power on,active,False,
oc-ctrl-jr-0,server-32,ACTIVE,-,Running,cp=172.31.0.7,power on,active,False,192.168.117.33
oc-comp-jr-1,server-10,ACTIVE,-,Running,cp=172.31.0.8,power on,active,False,

how gigantic are these files ?

if totaling less than maybe 3-4 GB, i'd perhaps suggest just load each file into the awk in its entirety, and leverage the associative arrays that are basically DB-indices already.

might be slightly less hectic than trying to keep up with that multi-way file join. Unless Unicode is a concern, or gensub( ) is is indispensable, consider running those exact codes suggested by others in mawk1.3.4 and mawk2-beta.

It's quite surreal seeing a dinosaur age scripting language beat tr, cut, sed, grep, at their own game, in quite a good chunk of my daily use cases.